DVR to delete router namespaces for service ports

Earlier merge that enabled LBaaS in DVR with review #114141
had not covered the removal of DVR router namespace on
VIP Port deletion in ml2 plugin.

Here we fix the ml2 plugin to attempt namespace removal for
all dvr serviced ports.

Change-Id: Ie7930ebedb12212886d45294132fefff7296e104
Closes-Bug: #1364839
Merge "DVR to delete router namespaces for service ports"