bpf: tcp: Guard declarations with CONFIG_NET_SOCK_MSG

tcp_bpf.c is only included in the build if CONFIG_NET_SOCK_MSG is
selected. The declaration should therefore be guarded as such.
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200309111243.6982-5-lmb@cloudflare.com

include/net/tcp.h

@@ -2195,6 +2195,7 @@ void tcp_update_ulp(struct sock *sk, struct proto *p,
 struct sk_msg;
 struct sk_psock;
 
+#ifdef CONFIG_NET_SOCK_MSG
 int tcp_bpf_init(struct sock *sk);
 int tcp_bpf_sendmsg_redir(struct sock *sk, struct sk_msg *msg, u32 bytes,
 			  int flags);
@@ -2202,13 +2203,12 @@ int tcp_bpf_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		    int nonblock, int flags, int *addr_len);
 int __tcp_bpf_recvmsg(struct sock *sk, struct sk_psock *psock,
 		      struct msghdr *msg, int len, int flags);
-#ifdef CONFIG_NET_SOCK_MSG
 void tcp_bpf_clone(const struct sock *sk, struct sock *newsk);
 #else
 static inline void tcp_bpf_clone(const struct sock *sk, struct sock *newsk)
 {
 }
-#endif
+#endif /* CONFIG_NET_SOCK_MSG */
 
 /* Call BPF_SOCK_OPS program that returns an int. If the return value
  * is < 0, then the BPF op failed (for example if the loaded BPF