tcp: Fix MD5 signature checking on IPv4 mapped sockets

Fix MD5 signature checking so that an IPv4 active open
to an IPv6 socket can succeed.  In particular, use the
correct address family's signature generation function
for the SYN/ACK.

Reported-by:   Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: John Dykstra <john.dykstra1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_ipv4.c

@@ -1160,6 +1160,7 @@ struct request_sock_ops tcp_request_sock_ops __read_mostly = {
 #ifdef CONFIG_TCP_MD5SIG
 static struct tcp_request_sock_ops tcp_request_sock_ipv4_ops = {
 	.md5_lookup	=	tcp_v4_reqsk_md5_lookup,
+	.calc_md5_hash	=	tcp_v4_md5_hash_skb,
 };
 #endif