IPv6 loopback ip is not displaying in fib entry

IPv6 loopback ip is not displaying in fib entry

Issue:
======
IPv6 address family type is not added to BGP VRF table
if external network is already been set with router-gw
before external network to Internet BGPVPN instance.

Solution:
=========
Added one more extra check when external network to
Internet BGPVPN association event call to check whether
external network is already been set with router-gw and
if that router has V6 subnet then set IPv6 address family
in the Internet BGPVPN instance. This logic will trigger
the subsequent event to update the BGP VRF table.

Signed-off-by: Karthikeyan Krishnan <karthikeyangceb007@gmail.com>
Change-Id: Ib382ac062c65ac3c974f72c125c8eb37c6f64f9d