bpf, tcp: Fix unused function warnings

If BPF_STREAM_PARSER is not set, gcc warns:

  net/ipv4/tcp_bpf.c:483:12: warning: 'tcp_bpf_sendpage' defined but not used [-Wunused-function]
  net/ipv4/tcp_bpf.c:395:12: warning: 'tcp_bpf_sendmsg' defined but not used [-Wunused-function]
  net/ipv4/tcp_bpf.c:13:13: warning: 'tcp_bpf_stream_read' defined but not used [-Wunused-function]

Moves the unused functions into the #ifdef CONFIG_BPF_STREAM_PARSER.

Fixes: f747632b ("bpf: sockmap: Move generic sockmap hooks from BPF TCP")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Lorenz Bauer <lmb@cloudflare.com>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200320023426.60684-2-yuehaibing@huawei.com

net/ipv4/tcp_bpf.c

@@ -10,19 +10,6 @@
 #include <net/inet_common.h>
 #include <net/tls.h>
 
-static bool tcp_bpf_stream_read(const struct sock *sk)
-{
-	struct sk_psock *psock;
-	bool empty = true;
-
-	rcu_read_lock();
-	psock = sk_psock(sk);
-	if (likely(psock))
-		empty = list_empty(&psock->ingress_msg);
-	rcu_read_unlock();
-	return !empty;
-}
-
 static int tcp_bpf_wait_data(struct sock *sk, struct sk_psock *psock,
 			     int flags, long timeo, int *err)
 {
@@ -298,6 +285,20 @@ int tcp_bpf_sendmsg_redir(struct sock *sk, struct sk_msg *msg,
 }
 EXPORT_SYMBOL_GPL(tcp_bpf_sendmsg_redir);
 
+#ifdef CONFIG_BPF_STREAM_PARSER
+static bool tcp_bpf_stream_read(const struct sock *sk)
+{
+	struct sk_psock *psock;
+	bool empty = true;
+
+	rcu_read_lock();
+	psock = sk_psock(sk);
+	if (likely(psock))
+		empty = list_empty(&psock->ingress_msg);
+	rcu_read_unlock();
+	return !empty;
+}
+
 static int tcp_bpf_send_verdict(struct sock *sk, struct sk_psock *psock,
 				struct sk_msg *msg, int *copied, int flags)
 {
@@ -528,7 +529,6 @@ static int tcp_bpf_sendpage(struct sock *sk, struct page *page, int offset,
 	return copied ? copied : err;
 }
 
-#ifdef CONFIG_BPF_STREAM_PARSER
 enum {
 	TCP_BPF_IPV4,
 	TCP_BPF_IPV6,