[build]: support submodule patching for SONIC_DPKG_DEBS (#619)

slave.mk

@@ -171,10 +171,14 @@ $(addprefix $(DEBS_PATH)/, $(SONIC_DPKG_DEBS)) : $(DEBS_PATH)/% : .platform $$(a
 	$(HEADER)
 	# Build project and take package
 	rm -f $($*_SRC_PATH)/debian/*.debhelper.log
+	# apply series of patches if exist
+	if [ -f $($*_SRC_PATH).patch/series ]; then pushd $($*_SRC_PATH) && QUILT_PATCHES=../$(notdir $($*_SRC_PATH)).patch quilt push -a; popd; fi
 	pushd $($*_SRC_PATH) $(LOG)
 	[ ! -f ./autogen.sh ] || ./autogen.sh $(LOG)
 	dpkg-buildpackage -rfakeroot -b -us -uc $(LOG)
 	popd $(LOG)
+	# clean up
+	if [ -f $($*_SRC_PATH).patch/series ]; then pushd $($*_SRC_PATH) && quilt pop -a -f; popd; fi
 	mv $(addprefix $($*_SRC_PATH)/../, $* $($*_DERIVED_DEBS) $($*_EXTRA_DEBS)) $(DEBS_PATH) $(LOG)
 	$(FOOTER)