mptcp: use adding up size to get ADD_ADDR length

This patch uses adding up size to get the ADD_ADDR suboption length rather
than returning the ADD_ADDR size constants.

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Geliang Tang <geliangtang@gmail.com>

net/mptcp/protocol.h

@@ -578,10 +578,14 @@ static inline bool mptcp_pm_should_rm_signal(struct mptcp_sock *msk)
 
 static inline unsigned int mptcp_add_addr_len(int family, bool echo)
 {
-	if (family == AF_INET)
-		return echo ? TCPOLEN_MPTCP_ADD_ADDR_BASE
-			    : TCPOLEN_MPTCP_ADD_ADDR;
-	return echo ? TCPOLEN_MPTCP_ADD_ADDR6_BASE : TCPOLEN_MPTCP_ADD_ADDR6;
+	u8 len = TCPOLEN_MPTCP_ADD_ADDR_BASE;
+
+	if (family == AF_INET6)
+		len = TCPOLEN_MPTCP_ADD_ADDR6_BASE;
+	if (!echo)
+		len += MPTCPOPT_THMAC_LEN;
+
+	return len;
 }
 
 bool mptcp_pm_add_addr_signal(struct mptcp_sock *msk, unsigned int remaining,