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/include/net/addrconf.h b/include/net/addrconf.h
index 87981cd..b8b1643 100644
--- a/include/net/addrconf.h
+++ b/include/net/addrconf.h
@@ -55,6 +55,7 @@
 struct in6_validator_info {
 	struct in6_addr		i6vi_addr;
 	struct inet6_dev	*i6vi_dev;
+	struct netlink_ext_ack	*extack;
 };
 
 #define IN6_ADDR_HSIZE_SHIFT	4