mptcp: use MPTCP_SUBFLOW_NODATA

Set subflow->data_avail with the enum value MPTCP_SUBFLOW_NODATA, instead
of using 0 directly.

Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Geliang Tang <geliang.tang@suse.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/mptcp/subflow.c

@@ -1104,7 +1104,7 @@ static bool subflow_check_data_avail(struct sock *ssk)
 	struct sk_buff *skb;
 
 	if (!skb_peek(&ssk->sk_receive_queue))
-		WRITE_ONCE(subflow->data_avail, 0);
+		WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_NODATA);
 	if (subflow->data_avail)
 		return true;
 
@@ -1169,7 +1169,7 @@ static bool subflow_check_data_avail(struct sock *ssk)
 		subflow->reset_transient = 0;
 		subflow->reset_reason = MPTCP_RST_EMIDDLEBOX;
 		tcp_send_active_reset(ssk, GFP_ATOMIC);
-		WRITE_ONCE(subflow->data_avail, 0);
+		WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_NODATA);
 		return true;
 	}
 
@@ -1182,7 +1182,7 @@ static bool subflow_check_data_avail(struct sock *ssk)
 		subflow->reset_transient = 0;
 		subflow->reset_reason = MPTCP_RST_EMPTCP;
 		tcp_send_active_reset(ssk, GFP_ATOMIC);
-		WRITE_ONCE(subflow->data_avail, 0);
+		WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_NODATA);
 		return false;
 	}
 
@@ -1204,7 +1204,7 @@ bool mptcp_subflow_data_available(struct sock *sk)
 	if (subflow->map_valid &&
 	    mptcp_subflow_get_map_offset(subflow) >= subflow->map_data_len) {
 		subflow->map_valid = 0;
-		WRITE_ONCE(subflow->data_avail, 0);
+		WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_NODATA);
 
 		pr_debug("Done with mapping: seq=%u data_len=%u",
 			 subflow->map_subflow_seq,