net: Add extack to validator_info structs used for address notifier

Add extack to in_validator_info and in6_validator_info. Update the one
user of each, ipvlan, to return an error message for failures.

Only manual configuration of an address is plumbed in the IPv6 code path.

Signed-off-by: David Ahern <dsahern@gmail.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ipvlan/ipvlan_main.c b/drivers/net/ipvlan/ipvlan_main.c
index 6842739..f0ab55d 100644
--- a/drivers/net/ipvlan/ipvlan_main.c
+++ b/drivers/net/ipvlan/ipvlan_main.c
@@ -847,8 +847,11 @@
 
 	switch (event) {
 	case NETDEV_UP:
-		if (ipvlan_addr_busy(ipvlan->port, &i6vi->i6vi_addr, true))
+		if (ipvlan_addr_busy(ipvlan->port, &i6vi->i6vi_addr, true)) {
+			NL_SET_ERR_MSG(i6vi->extack,
+				       "Address already assigned to an ipvlan device");
 			return notifier_from_errno(-EADDRINUSE);
+		}
 		break;
 	}
 
@@ -917,8 +920,11 @@
 
 	switch (event) {
 	case NETDEV_UP:
-		if (ipvlan_addr_busy(ipvlan->port, &ivi->ivi_addr, false))
+		if (ipvlan_addr_busy(ipvlan->port, &ivi->ivi_addr, false)) {
+			NL_SET_ERR_MSG(ivi->extack,
+				       "Address already assigned to an ipvlan device");
 			return notifier_from_errno(-EADDRINUSE);
+		}
 		break;
 	}