[202205] Add dhcpmon submodule and latest updates

.gitmodules

@@ -112,3 +112,6 @@
 [submodule "src/dhcprelay"]
 	path = src/dhcprelay
 	url = https://github.com/sonic-net/sonic-dhcp-relay.git
+[submodule "src/dhcpmon"]
+	path = src/dhcpmon
+	url = https://github.com/sonic-net/sonic-dhcpmon.git

rules/dhcpmon.dep

@@ -2,9 +2,10 @@
 SPATH       := $($(SONIC_DHCPMON)_SRC_PATH)
 DEP_FILES   := $(SONIC_COMMON_FILES_LIST) rules/dhcpmon.mk rules/dhcpmon.dep   
 DEP_FILES   += $(SONIC_COMMON_BASE_FILES_LIST)
-DEP_FILES   += $(shell git ls-files $(SPATH))
+SMDEP_FILES := $(addprefix $(SPATH)/,$(shell cd $(SPATH) && git ls-files))
 
 $(SONIC_DHCPMON)_CACHE_MODE  := GIT_CONTENT_SHA 
 $(SONIC_DHCPMON)_DEP_FLAGS   := $(SONIC_COMMON_FLAGS_LIST)
 $(SONIC_DHCPMON)_DEP_FILES   := $(DEP_FILES)
-
+$(SONIC_DHCPMON)_SMDEP_FILES := $(SMDEP_FILES)
+$(SONIC_DHCPMON)_SMDEP_PATHS := $(SPATH)