udp: Fix a memory leak in udp6_send()

Reviewed by:	glebius
MFC after:	3 days
Differential Revision:	https://reviews.freebsd.org/D38993

sys/netinet6/udp6_usrreq.c

@@ -766,10 +766,10 @@ udp6_send(struct socket *so, int flags_arg, struct mbuf *m,
 		 * Given this is either an IPv6-only socket or no INET is
 		 * supported we will fail the send if the given destination
 		 * address is a v4mapped address.
-		 *
-		 * XXXGL: do we leak m and control?
 		 */
 		INP_UNLOCK(inp);
+		m_freem(m);
+		m_freem(control);
 		return (EINVAL);
 	}