neigh: Netlink notification for administrative NUD state change

The neighbour code sends up an RTM_NEWNEIGH netlink notification if
the NUD state of a neighbour cache entry is changed by a timer (e.g.
from REACHABLE to STALE), even if the lladdr of the entry has not
changed.

But an administrative change to the the NUD state of a neighbour cache
entry that does not change the lladdr (e.g. via "ip -4 neigh change
...  nud ...") does not trigger a netlink notification.  This means
that netlink listeners will not hear about administrative NUD state
changes such as from a resolved state to PERMANENT.

This patch changes the neighbor code to generate an RTM_NEWNEIGH
message when the NUD state of an entry is changed administratively.

Signed-off-by: Bob Gilligan <gilligan@aristanetworks.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/neighbour.c

@@ -1161,6 +1161,7 @@ int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new,
 						 neigh->parms->reachable_time :
 						 0)));
 		neigh->nud_state = new;
+		notify = 1;
 	}
 
 	if (lladdr != neigh->ha) {