neigh: Send netevent after marking neigh as dead

neigh_cleanup_and_release() is always called after marking a neighbour
as dead, but it only notifies user space and not in-kernel listeners of
the netevent notification chain.

This can cause multiple problems. In my specific use case, it causes the
listener (a switch driver capable of L3 offloads) to believe a neighbour
entry is still valid, and is thus erroneously kept in the device's
table.

Fix that by sending a netevent after marking the neighbour as dead.

Fixes: a6bf9e9 ("mlxsw: spectrum_router: Offload neighbours based on NUD state change")
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/neighbour.c

@@ -100,6 +100,7 @@ static void neigh_cleanup_and_release(struct neighbour *neigh)
 		neigh->parms->neigh_cleanup(neigh);
 
 	__neigh_notify(neigh, RTM_DELNEIGH, 0);
+	call_netevent_notifiers(NETEVENT_NEIGH_UPDATE, neigh);
 	neigh_release(neigh);
 }