zebra: implement per-route mtu handling

This commits allow overriding MTU using netlink attributes on
per-route basis. This is useful for routing protocols that can
advertice prefix specific MTUs between routers (e.g. NHRP).

Signed-off-by: Timo Teräs <timo.teras@iki.fi>
diff --git a/zebra/connected.c b/zebra/connected.c
index 244f291..84b0d1c 100644
--- a/zebra/connected.c
+++ b/zebra/connected.c
@@ -192,10 +192,10 @@
     return;
 
   rib_add_ipv4 (ZEBRA_ROUTE_CONNECT, 0, &p, NULL, NULL, ifp->ifindex,
-       ifp->vrf_id, RT_TABLE_MAIN, ifp->metric, 0, SAFI_UNICAST);
+       ifp->vrf_id, RT_TABLE_MAIN, ifp->metric, 0, 0, SAFI_UNICAST);
 
   rib_add_ipv4 (ZEBRA_ROUTE_CONNECT, 0, &p, NULL, NULL, ifp->ifindex,
-       ifp->vrf_id, RT_TABLE_MAIN, ifp->metric, 0, SAFI_MULTICAST);
+       ifp->vrf_id, RT_TABLE_MAIN, ifp->metric, 0, 0, SAFI_MULTICAST);
 
   rib_update (ifp->vrf_id);
 }
@@ -356,7 +356,7 @@
 #endif
 
   rib_add_ipv6 (ZEBRA_ROUTE_CONNECT, 0, &p, NULL, ifp->ifindex, ifp->vrf_id,
-                RT_TABLE_MAIN, ifp->metric, 0, SAFI_UNICAST);
+                RT_TABLE_MAIN, ifp->metric, 0, 0, SAFI_UNICAST);
 
   rib_update (ifp->vrf_id);
 }