When deleting a network make sure to remove all linked ports
When deleting a network make sure to remove all linked ports

Change-Id: I6b7ce082e6d185e870c82d76dd08278b8485cfc3
Closes-bug: #1560895

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