mptcp: update userspace pm subflows info

Increase pm subflows counter when userspace pm creates a new subflow,
and decrease the counter when it closes a subflow.

Closes: multipath-tcp/mptcp_net-next#329
Signed-off-by: Geliang Tang <geliang.tang@suse.com>

net/mptcp/pm_userspace.c

@@ -302,6 +302,10 @@ int mptcp_nl_cmd_sf_create(struct sk_buff *skb, struct genl_info *info)
 		goto create_err;
 	}
 
+	spin_lock_bh(&msk->pm.lock);
+	msk->pm.subflows++;
+	spin_unlock_bh(&msk->pm.lock);
+
 	lock_sock(sk);
 
 	err = __mptcp_subflow_connect(sk, &addr_l, &addr_r);
@@ -424,6 +428,9 @@ int mptcp_nl_cmd_sf_destroy(struct sk_buff *skb, struct genl_info *info)
 		mptcp_subflow_shutdown(sk, ssk, RCV_SHUTDOWN | SEND_SHUTDOWN);
 		mptcp_close_ssk(sk, ssk, subflow);
 		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_RMSUBFLOW);
+		spin_lock_bh(&msk->pm.lock);
+		msk->pm.subflows--;
+		spin_unlock_bh(&msk->pm.lock);
 		err = 0;
 	} else {
 		err = -ESRCH;