udp: make some messages more descriptive

In the UDP code there are two leftover error messages with very few meaning.
Replace them with a more descriptive error message as some users
reported them as "strange network error".

Signed-off-by: Matteo Croce <mcroce@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/udp.c

@@ -1061,7 +1061,7 @@ back_from_confirm:
 		/* ... which is an evident application bug. --ANK */
 		release_sock(sk);
 
-		net_dbg_ratelimited("cork app bug 2\n");
+		net_dbg_ratelimited("socket already corked\n");
 		err = -EINVAL;
 		goto out;
 	}
@@ -1144,7 +1144,7 @@ int udp_sendpage(struct sock *sk, struct page *page, int offset,
 	if (unlikely(!up->pending)) {
 		release_sock(sk);
 
-		net_dbg_ratelimited("udp cork app bug 3\n");
+		net_dbg_ratelimited("cork failed\n");
 		return -EINVAL;
 	}