bgpd: Don't necessarily ignore interface callbacks

bgpd: Don't necessarily ignore interface callbacks

In bgp if we have not configured bgp we were ignoring
interface based callbacks.  Leading to states where
we may not be processing interface information.
Leading to states where we do not actually keep
ifp data.  As an example:

Suppose vrf A and vrf B.  A has interface swp1.
At the same time we only have a `router bgp 9 vrf B`
When we received the callback for moving swp1
from vrf A to vrf B we were not processing the
move at all and BGP would not consider the interface
part of vrf B at all.

This commit makes bgp pay attention to interface
events irrelevant if bgp is using that vrf.  This
is now consistent with how the lib/if* expects
to work and the rest of the daemons in FRR.

Signed-off-by: Donald Sharp <sharpd@cumulsnetworks.com>