nhrpd: fix ignore neighbor stale message

The 'used' field of NHRP cache entries goes to false every
time it receives a netlink STALE message. Consequently, the
cache entry appears as unused until the reception of a PROBE
message triggers the neighbor entry re-configuration that
changes the entry to REACHABLE.

> '# show ip nhrp cache' command before receiving STALE message.
> Iface    Type     Protocol                 NBMA                     Claimed NBMA             Flags  Identity
> gre1     nhs      11.255.255.1             10.125.0.1               10.125.0.1                UT     west
> # ip monitor neigh dev gre1
> 10.125.0.1 lladdr de:ed:02:05:3c:b5 STALE
>
> '# show ip nhrp cache' command after sending STALE message.
> Iface    Type     Protocol                 NBMA                     Claimed NBMA             Flags  Identity
> gre1     nhs      11.255.255.1             10.125.0.1               10.125.0.1                T     west

Fix this by ignoring the STALE state, and do not change the cache
entry 'used' flag.

Signed-off-by: Philippe Guibert <[email protected]>

nhrpd/netlink_arp.c

@@ -203,8 +203,10 @@ int nhrp_neighbor_operation(ZAPI_CALLBACK_ARGS)
 		}
 	} else {
 		state = (cmd == ZEBRA_NEIGH_ADDED) ? ndm_state
-						   : ZEBRA_NEIGH_STATE_FAILED;
-		nhrp_cache_set_used(c, state == ZEBRA_NEIGH_STATE_REACHABLE);
+			: ZEBRA_NEIGH_STATE_FAILED;
+		if (ndm_state != ZEBRA_NEIGH_STATE_STALE)
+			nhrp_cache_set_used(c,
+					    state == ZEBRA_NEIGH_STATE_REACHABLE);
 	}
 	return 0;
 }