[FRR]: Use stg in a proper way. (#3589)

* [FRR]: Use stg in a proper way.

Signed-off-by: wangshengjun <wangshengjun@asterfusion.com>

* [FRR]restore the detach status for frr submodule after finish patching

Signed-off-by: wangshengjun <wangshengjun@asterfusion.com>

* [FRR]use the 'FRR_VERSION' exported from 'rule/frr.mk'.

Signed-off-by: wangshengjun <wangshengjun@asterfusion.com>

src/sonic-frr/Makefile

@@ -4,20 +4,23 @@ SHELL = /bin/bash
 
 MAIN_TARGET = $(FRR)
 DERIVED_TARGET = $(FRR_PYTHONTOOLS) $(FRR_DBG) $(FRR_SNMP) $(FRR_SNMP_DBG)
-BRANCH = $(shell date +%Y%m%d\.%H%M%S)
+FRR_BRANCH = frr/$(FRR_VERSION)
+STG_BRANCH = stg_temp
 
 $(addprefix $(DEST)/, $(MAIN_TARGET)): $(DEST)/% :
 	# Build the package
-	pushd ./frr	
-	git checkout -b $(BRANCH) origin/frr/7.1
-	stg init
+	pushd ./frr
+	git checkout -b $(FRR_BRANCH) origin/$(FRR_BRANCH)
+	stg branch --create $(STG_BRANCH) $(FRR_BRANCH)
 	stg import -s ../patch/series
 	tools/tarsource.sh -V -e '-sonic'
 	dpkg-buildpackage -rfakeroot -b -us -uc -Ppkg.frr.nortrlib -j$(SONIC_CONFIG_MAKE_JOBS)
 	stg undo
 	git clean -xfdf
-	git checkout frr/7.1
-	git branch -D $(BRANCH)
+	git checkout $(FRR_BRANCH)
+	stg branch --delete $(STG_BRANCH)
+	git rev-parse --short HEAD | xargs git checkout
+	git branch -D $(FRR_BRANCH)
 	popd
 	mv $(DERIVED_TARGET) $* $(DEST)/