[docker-sflow]: upgrade docker-sflow on buster (#4904)

dockers/docker-sflow/Dockerfile.j2

@@ -1,5 +1,5 @@
 {% from "dockers/dockerfile-macros.j2" import install_debian_packages, install_python_wheels, copy_files %}
-FROM docker-config-engine-stretch
+FROM docker-config-engine-buster
 
 ARG docker_container_name
 RUN [ -f /etc/rsyslog.conf ] && sed -ri "s/%syslogtag%/$docker_container_name#%syslogtag%/;" /etc/rsyslog.conf

rules/docker-sflow.mk

@@ -7,22 +7,20 @@ DOCKER_SFLOW_DBG = $(DOCKER_SFLOW_STEM)-$(DBG_IMAGE_MARK).gz
 $(DOCKER_SFLOW)_PATH = $(DOCKERS_PATH)/$(DOCKER_SFLOW_STEM)
 
 $(DOCKER_SFLOW)_DEPENDS += $(SWSS) $(HSFLOWD) $(SFLOWTOOL) $(PSAMPLE)
-$(DOCKER_SFLOW)_DBG_DEPENDS = $($(DOCKER_CONFIG_ENGINE_STRETCH)_DBG_DEPENDS)
+$(DOCKER_SFLOW)_DBG_DEPENDS = $($(DOCKER_CONFIG_ENGINE_BUSTER)_DBG_DEPENDS)
 $(DOCKER_TEAMD)_DBG_DEPENDS += $(SWSS_DBG) $(LIBSWSSCOMMON_DBG)
-$(DOCKER_SFLOW)_DBG_IMAGE_PACKAGES = $($(DOCKER_CONFIG_ENGINE_STRETCH)_DBG_IMAGE_PACKAGES)
+$(DOCKER_SFLOW)_DBG_IMAGE_PACKAGES = $($(DOCKER_CONFIG_ENGINE_BUSTER)_DBG_IMAGE_PACKAGES)
 
-$(DOCKER_SFLOW)_LOAD_DOCKERS += $(DOCKER_CONFIG_ENGINE_STRETCH)
+$(DOCKER_SFLOW)_LOAD_DOCKERS += $(DOCKER_CONFIG_ENGINE_BUSTER)
 
 SONIC_DOCKER_IMAGES += $(DOCKER_SFLOW)
 ifeq ($(ENABLE_SFLOW), y)
 SONIC_INSTALL_DOCKER_IMAGES += $(DOCKER_SFLOW)
-SONIC_STRETCH_DOCKERS += $(DOCKER_SFLOW)
 endif
 
 SONIC_DOCKER_DBG_IMAGES += $(DOCKER_SFLOW_DBG)
 ifeq ($(ENABLE_SFLOW), y)
 SONIC_INSTALL_DOCKER_DBG_IMAGES += $(DOCKER_SFLOW_DBG)
-SONIC_STRETCH_DBG_DOCKERS += $(DOCKER_SFLOW_DBG)
 endif
 
 $(DOCKER_SFLOW)_CONTAINER_NAME = sflow