tcpv6: fix option space offsets with md5

More breakage :-), part of timestamps just were previously
overwritten.
Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/tcp_ipv6.c

@@ -1088,7 +1088,7 @@ static void tcp_v6_send_ack(struct sk_buff *skb, u32 seq, u32 ack, u32 win, u32
 		*topt++ = htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) |
 				(TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP);
 		*topt++ = htonl(tcp_time_stamp);
-		*topt = htonl(ts);
+		*topt++ = htonl(ts);
 	}
 
 #ifdef CONFIG_TCP_MD5SIG