Fix more unused variables and enable unused-but-set-variable errors.

Add -Werror=unused-but-set-variable to our default compiler flags and fix

```
epan/dissectors/packet-dcerpc-frsrpc.c:709:10: error: variable 'nb_chunk' set but not used [-Werror,-Wunused-but-set-variable]
        guint32 nb_chunk = 0;
                ^
```

```
epan/dissectors/packet-dcom-oxid.c:175:13: error: variable 'u32ItemIdx' set but not used [-Werror,-Wunused-but-set-variable]
    guint32 u32ItemIdx;
            ^
```

```
epan/dissectors/packet-l2tp.c:1775:104: error: parameter 'ccid' set but not used [-Werror,-Wunused-but-set-parameter]
static int dissect_l2tp_ericsson_avps(tvbuff_t *tvb, packet_info *pinfo _U_, proto_tree *tree, guint32 ccid)
                                                                                                       ^
```

```
epan/dissectors/packet-ldp.c:1922:19: error: variable 'ix' set but not used [-Werror,-Wunused-but-set-variable]
    guint8        ix;
                  ^
```

```
epan/dissectors/packet-nas_5gs.c:4757:14: error: variable 'curr_len' set but not used [-Werror,-Wunused-but-set-variable]
    guint i, curr_len;
             ^
```

```
epan/dissectors/packet-per.c:1769:6: error: variable 'extension_addition_entries' set but not used [-Werror,-Wunused-but-set-variable]
        int extension_addition_entries;
            ^
```

```
epan/dissectors/packet-rtitcp.c:618:11: error: variable 'messages_count' set but not used [-Werror,-Wunused-but-set-variable]
    guint messages_count, offset;
          ^
```

```
epan/dissectors/packet-tcp.c:2130:9: error: variable 'ackcount' set but not used [-Werror,-Wunused-but-set-variable]
    int ackcount;
        ^
epan/dissectors/packet-tcp.c:3317:12: error: variable 'nbOptionsChanged' set but not used [-Werror,-Wunused-but-set-variable]
    guint8 nbOptionsChanged = 0;
           ^
```

```
epan/dissectors/packet-zbee-zcl-se.c:11802:15: error: variable 'i' set but not used [-Werror,-Wunused-but-set-variable]
    for (gint i = 0; tvb_reported_length_remaining(tvb, *offset) >= 5; i++) {
              ^
```

```
ui/iface_lists.c:142:23: error: variable 'linktype_count' set but not used [-Werror,-Wunused-but-set-variable]
    gint              linktype_count;
                      ^
```

```
ui/voip_calls.c:456:15: error: variable 'item_num' set but not used [-Werror,-Wunused-but-set-variable]
    guint     item_num;
              ^
```

```
file.c:572:17: error: variable 'count' set but not used [-Werror,-Wunused-but-set-variable]
        guint32 count             = 0;
                ^
```

```
file.c:3667:24: warning: cast from 'const unsigned char *' to 'unsigned char *' drops const qualifier [-Wcast-qual]
        pd = (guint8 *)ws_mempbrk_exec(pd, buf_end - pd, pattern, &c_char);
                       ^
```

```
ui/qt/io_graph_dialog.cpp:1932:60: error: variable 'mavg_right' set but not used [-Werror,-Wunused-but-set-variable]
    unsigned int mavg_in_average_count = 0, mavg_left = 0, mavg_right = 0;
                                                           ^
```

```
ui/qt/stats_tree_dialog.cpp:166:9: error: variable 'node_count' set but not used [-Werror,-Wunused-but-set-variable]
    int node_count = 0;
        ^
```

```
ui/qt/models/profile_model.cpp:1142:13: error: variable 'entryCount' set but not used [-Werror,-Wunused-but-set-variable]
        int entryCount = 0;
            ^
```

1 files changed, 2 insertions, 3 deletions

diff --git a/epan/dissectors/packet-dcerpc-frsrpc.c b/epan/dissectors/packet-dcerpc-frsrpc.c
index 5d506f487b..b733ae200b 100644
--- a/epan/dissectors/packet-dcerpc-frsrpc.c
+++ b/epan/dissectors/packet-dcerpc-frsrpc.c
@@ -663,7 +663,7 @@ frsrpc_dissect_struct_CommPktChunk(tvbuff_t *tvb _U_, int offset _U_, packet_inf
 		item = proto_tree_add_item(parent_tree, hf_index, tvb, offset, -1, TRUE);
 		tree = proto_item_add_subtree(item, ett_frsrpc_frsrpc_CommPktChunk);
 	}
-	
+
 	offset = frsrpc_dissect_element_CommPktChunk_type(tvb, offset, pinfo, tree, di, drep, &type);
 	offset = frsrpc_dissect_element_CommPktChunk_data(tvb, offset, pinfo, tree, di, drep, &type);
 	for (i=0; frsrpc_frsrpc_CommPktChunkType_vals[i].strptr; i++) {
@@ -706,14 +706,13 @@ frsrpc_dissect_enum_CommPktCommand(tvbuff_t *tvb _U_, int offset _U_, packet_inf
 static int
 frsrpc_dissect_struct_frsrpc_CommPktChunkCtr(tvbuff_t *tvb, int offset, packet_info *pinfo, proto_tree *tree, dcerpc_info* di, guint8 *drep _U_, int hf_index, guint32 param _U_)
 {
-	guint32 nb_chunk = 0;
 	guint32 remaining = tvb_reported_length_remaining(tvb, offset);
 	int align_status = di->no_align;
 	if (remaining > 0) {
 		proto_item *item = proto_tree_add_item(tree, hf_index, tvb, offset, -1, TRUE);
 		proto_tree *subtree = proto_item_add_subtree(item, ett_ChunkCtr);
 		di->no_align = 1;
-		for(nb_chunk = 0; remaining > 0; nb_chunk++) {
+		while (remaining > 0) {
 			offset = frsrpc_dissect_struct_CommPktChunk(tvb, offset, pinfo, subtree, di, drep, hf_CommPktChunk, param);
 			remaining = tvb_reported_length_remaining(tvb, offset);
 		}