[frr]: Fix for missing dependency in frr module (sonic-net#6094)

The soinc-frr module has src/sonic-frr/frr submodule. The FRR sub module dependency files are not added to the DPKG file tracking. The patch includes the following.

- Included the submodule dependency files
- Removes the symbolic files.

rules/frr.dep

@@ -2,9 +2,24 @@
 SPATH       := $($(FRR)_SRC_PATH)
 DEP_FILES   := $(SONIC_COMMON_FILES_LIST) rules/frr.mk rules/frr.dep   
 DEP_FILES   += $(SONIC_COMMON_BASE_FILES_LIST)
-SMDEP_FILES := $(addprefix $(SPATH)/,$(shell cd $(SPATH) && git ls-files))
+DEP_FILES   += $(addprefix $(SPATH)/,$(shell cd $(SPATH) && git ls-files |grep -Ev '^frr$$$$'))
+
+# Account for source files under the frr submodule directory as well.
+# Remove all the symbolic link files
+FRR_SPATH   := $(SPATH)/frr
+SMDEP_FILES := $(addprefix $(FRR_SPATH)/,$(shell cd $(FRR_SPATH) && git ls-files \
+			| grep -Ev -e 'debian/changelog$$$$' \
+			-e '^tests/topotests/bgp_instance_del_test/ce[0-9]$$$$' \
+			-e '^tests/topotests/bgp_instance_del_test/r[0-9]$$$$' \
+			-e '^tests/topotests/bgp_instance_del_test/scripts$$$$' \
+			-e '^tests/topotests/bgp_instance_del_test/customize.py$$$$' \
+			-e '^tests/topotests/bgp_rfapi_basic_sanity_config2/customize.py$$$$' \
+			-e '^tests/topotests/bgp_rfapi_basic_sanity_config2/scripts$$$$' \
+			-e '^tests/topotests/bgp_rfapi_basic_sanity_config2/test_bgp_rfapi_basic_sanity_config2.py$$$$' \
+			))
 
 $(FRR)_CACHE_MODE  := GIT_CONTENT_SHA 
 $(FRR)_DEP_FLAGS   := $(SONIC_COMMON_FLAGS_LIST)
 $(FRR)_DEP_FILES   := $(DEP_FILES)
-
+$(FRR)_SMDEP_FILES := $(SMDEP_FILES)
+$(FRR)_SMDEP_PATHS := $(FRR_SPATH)