dfilter: Allow writing references without curly braces

Allow references without braces, for a less cluttered syntax:

    Filter:
     frame.number > $frame.number

    Instructions:
     0000 READ_TREE        frame.number     -> R0
     0001 IF_FALSE_GOTO    5
     0002 READ_REFERENCE   ${frame.number}  -> R1
     0003 IF_FALSE_GOTO    5
     0004 ANY_GT           R0 > R1
     0005 RETURN

The original syntax of ${reference} came from macros but the
braces don't add much. In any case they are still allowed.

1 files changed, 10 insertions, 0 deletions

diff --git a/test/suite_dfilter/group_syntax.py b/test/suite_dfilter/group_syntax.py
index c118e498f3..89fc5596c1 100644
--- a/test/suite_dfilter/group_syntax.py
+++ b/test/suite_dfilter/group_syntax.py
@@ -343,6 +343,16 @@ class TestDfilterFieldReference:
         # select frame 1, expect 1 frames out of 2.
         checkDFilterCountWithSelectedFrame(dfilter, 1, 1)
 
+    def test_ref_3(self, checkDFilterCountWithSelectedFrame):
+        dfilter = 'frame.number < $frame.number'
+        # select frame 2, expect 1 frames out of 2.
+        checkDFilterCountWithSelectedFrame(dfilter, 1, 2)
+
+    def test_ref_4(self, checkDFilterCountWithSelectedFrame):
+        dfilter = 'ip.src#3 == $ip.src#4'
+        # select frame 1, expect 1 frames out of 2.
+        checkDFilterCountWithSelectedFrame(dfilter, 1, 1)
+
 class TestDfilterLayer:
     trace_file = "ipoipoip.pcap"