tcp md5sig: Share MD5 Signature option parser between IPv4 and IPv6.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 633147c..b1c4b78 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -399,6 +399,8 @@
 						  struct tcp_options_received *opt_rx,
 						  int estab);
 
+extern u8			*tcp_parse_md5sig_option(struct tcphdr *th);
+
 /*
  *	TCP v4 functions exported for the inet6 API
  */