bridge: check for zero ether address in fdb add

The check for all-zero ether address was removed from rtnetlink core,
since Vxlan uses all-zero ether address to signify default address.
Need to add check back in for bridge.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

net/bridge/br_fdb.c

@@ -707,6 +707,11 @@ int br_fdb_add(struct ndmsg *ndm, struct nlattr *tb[],
 		}
 	}
 
+	if (is_zero_ether_addr(addr)) {
+		pr_info("bridge: RTM_NEWNEIGH with invalid ether address\n");
+		return -EINVAL;
+	}
+
 	p = br_port_get_rtnl(dev);
 	if (p == NULL) {
 		pr_info("bridge: RTM_NEWNEIGH %s not a bridge port\n",