tcp: md5: add TCP_MD5SIG_EXT socket option to set a key address prefix

Replace first padding in the tcp_md5sig structure with a new flag field
and address prefix length so it can be specified when configuring a new
key for TCP MD5 signature. The tcpm_flags field will only be used if the
socket option is TCP_MD5SIG_EXT to avoid breaking existing programs, and
tcpm_prefixlen only when the TCP_MD5SIG_FLAG_PREFIX flag is set.

Signed-off-by: Bob Gilligan <gilligan@arista.com>
Signed-off-by: Eric Mowat <mowat@arista.com>
Signed-off-by: Ivan Delalande <colona@arista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 11e4ee2..058f509 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2714,8 +2714,9 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
 
 #ifdef CONFIG_TCP_MD5SIG
 	case TCP_MD5SIG:
+	case TCP_MD5SIG_EXT:
 		/* Read the IP->Key mappings from userspace */
-		err = tp->af_specific->md5_parse(sk, optval, optlen);
+		err = tp->af_specific->md5_parse(sk, optname, optval, optlen);
 		break;
 #endif
 	case TCP_USER_TIMEOUT: