tcp: rework {__,}tcp_ecn_check_ce() -> tcp_data_ecn_check()

Rename tcp_ecn_check_ce to tcp_data_ecn_check as it is
called only for data segments, not for ACKs (with AccECN,
also ACKs may get ECN bits).

The extra "layer" in tcp_ecn_check_ce() function just
checks for ECN being enabled, that can be moved into
tcp_ecn_field_check rather than having the __ variant.

No functional changes.

Signed-off-by: Ilpo Järvinen <[e-mail]>
Signed-off-by: Chia-Yu Chang <[e-mail]>
Reviewed-by: Eric Dumazet <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/tcp_input.c

···
 	tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR;
 }
 
-static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
+static void tcp_data_ecn_check(struct sock *sk, const struct sk_buff *skb)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
+
+	if (!(tcp_sk(sk)->ecn_flags & TCP_ECN_OK))
+		return;
 
 	switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
 	case INET_ECN_NOT_ECT:
···
 		tp->ecn_flags |= TCP_ECN_SEEN;
 		break;
 	}
-}
-
-static void tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
-{
-	if (tcp_sk(sk)->ecn_flags & TCP_ECN_OK)
-		__tcp_ecn_check_ce(sk, skb);
 }
 
 static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
···
 	icsk->icsk_ack.lrcvtime = now;
 	tcp_save_lrcv_flowlabel(sk, skb);
 
-	tcp_ecn_check_ce(sk, skb);
+	tcp_data_ecn_check(sk, skb);
 
 	if (skb->len >= 128)
 		tcp_grow_window(sk, skb, true);
···
 	bool fragstolen;
 
 	tcp_save_lrcv_flowlabel(sk, skb);
-	tcp_ecn_check_ce(sk, skb);
+	tcp_data_ecn_check(sk, skb);
 
 	if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);