zebra: let the route-map rule "match interface" work for VRFs

zebra: let the route-map rule "match interface" work for VRFs

Introduce a new "struct nexthop_vrfid" to specify a nexthop together
with the VRF ID it belongs to.

Thus in route_match_interface(), we can lookup the interface from
the correct VRF.

Signed-off-by: Feng Lu <lu.feng@6wind.com>
Reviewed-by: Alain Ritoux <alain.ritoux@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: Vincent JARDIN <vincent.jardin@6wind.com>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
Conflicts:
	zebra/zebra_rib.c
	zebra/zebra_routemap.c