dfilter: fix memleaks with functions and slice operator

Running tools/dfilter-test.py with LSan enabled resulted in 38 test
failures due to memory leaks from "fvalue_new". Problematic dfilters:
- Return values from functions, e.g. `len(data.data) > 8` (instruction
  CALL_FUNCTION invoking functions from epan/dfilter/dfunctions.c)
- Slice operator: `data.data[1:2] == aa:bb` (function mk_range)

These values end up in "registers", but as some values (from READ_TREE)
reference the proto tree, a new tracking flag ("owns_memory") is added.

Add missing tests for some functions and try to improve documentation.

Change-Id: I28e8cf872675d0a81ea7aa5fac7398257de3f47b
Reviewed-on: https://code.wireshark.org/review/27132
Petri-Dish: Peter Wu <peter@lekensteyn.nl>
Reviewed-by: Peter Wu <peter@lekensteyn.nl>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/tshark.c b/tshark.c
index 504aae4226..fec5266d63 100644
--- a/tshark.c
+++ b/tshark.c
@@ -2249,6 +2249,7 @@ clean_exit:
   wtap_cleanup();
   free_progdirs();
   cf_close(&cfile);
+  dfilter_free(dfcode);
   return exit_status;
 }