Trigger provider security group update for RA

For IPv6 subnets, router RA rule is added to compute node
to allow VM to accept RA from router interface on network node.
However, currently this is only done when router port which
sends RA is created *before* VM port is created.

This fix triggers provider security group rule update for IPv6 subnet
when router interface port is created or updated.

Change-Id: I7d950f12909a0c2a82b129279e6249b9fac80112
Closes-Bug: 1290252
Merge "Trigger provider security group update for RA"