net: ipv6: Add extack messages for route add failures

Add messages for non-obvious errors (e.g, no need to add text for malloc
failures or ENODEV failures). This mostly covers the annoying EINVAL errors
Some message strings violate the 80-columns but searchable strings need to
trump that rule.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index c1197e1..deea901 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -498,6 +498,8 @@ static struct fib6_node *fib6_add_1(struct fib6_node *root,
 		    !ipv6_prefix_equal(&key->addr, addr, fn->fn_bit)) {
 			if (!allow_create) {
 				if (replace_required) {
+					NL_SET_ERR_MSG(extack,
+						       "Can not replace route - no match found");
 					pr_warn("Can't replace route, no match found\n");
 					return ERR_PTR(-ENOENT);
 				}
@@ -544,6 +546,8 @@ static struct fib6_node *fib6_add_1(struct fib6_node *root,
 		 * That would keep IPv6 consistent with IPv4
 		 */
 		if (replace_required) {
+			NL_SET_ERR_MSG(extack,
+				       "Can not replace route - no match found");
 			pr_warn("Can't replace route, no match found\n");
 			return ERR_PTR(-ENOENT);
 		}