Fix links in the pluggable_pubsub doc
Fix links in the pluggable_pubsub doc

Change-Id: I26c550c2957fc942146b727ff2090b843d8df525

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