Fix empty ofport value
Fix empty ofport value

Closes-bug: #1568506
Change-Id: I98a10950c9d91bfe6c033d52fdcb66e29301dee5

openstack/dragonflow,FrankDuan/df_code,openstack/dragonflow,openstack/dragonflow,FrankDuan/df_code,FrankDuan/df_code