[build] Fix frr dpkg cache calculation issue on symbolic link file. (#16700)

Why I did it
Now build will fail on:

fatal: Unable to hash src/sonic-frr/frr/tests/topotests/grpc_basic/lib
fatal: Unable to hash src/sonic-frr/frr/tests/topotests/ospfapi/lib
make: *** [Makefile.cache:528: target/debs/buster/frr_8.5.1-sonic-0_amd64.deb.smdep] Error 123
make: *** Waiting for unfinished jobs....
Root cause is that these files are symbol links.
git hash-object can't hash symbol links.

Work item tracking
Microsoft ADO (number only): 25271730
How I did it
These two files are symbol links.
When calculate sha value, skip these two files.

rules/frr.dep

@@ -9,6 +9,8 @@ DEP_FILES   += $(addprefix $(SPATH)/,$(shell cd $(SPATH) && git ls-files |grep -
 FRR_SPATH   := $(SPATH)/frr
 SMDEP_FILES := $(addprefix $(FRR_SPATH)/,$(shell cd $(FRR_SPATH) && git ls-files \
 			| grep -Ev -e 'debian/changelog$$$$' \
+			-e '^tests/topotests/grpc_basic/lib$$$$' \
+			-e '^tests/topotests/ospfapi/lib$$$$' \
 			-e '^tests/topotests/bgp_instance_del_test/ce[0-9]$$$$' \
 			-e '^tests/topotests/bgp_instance_del_test/r[0-9]$$$$' \
 			-e '^tests/topotests/bgp_instance_del_test/scripts$$$$' \