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/include/net/tcp.h b/include/net/tcp.h
index 8f4076d..d0751b7 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1848,6 +1848,7 @@ struct tcp_sock_af_ops {
 					 const struct sock *sk,
 					 const struct sk_buff *skb);
 	int		(*md5_parse)(struct sock *sk,
+				     int optname,
 				     char __user *optval,
 				     int optlen);
 #endif