socket: fix unused-function warning

When procfs is disabled, the fdinfo code causes a harmless
warning:

net/socket.c:1000:13: error: 'sock_show_fdinfo' defined but not used [-Werror=unused-function]
 static void sock_show_fdinfo(struct seq_file *m, struct file *f)

Move the function definition up so we can use a single #ifdef
around it.

Fixes: b4653342 ("net: Allow to show socket-specific information in /proc/[pid]/fdinfo/[fd]")
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/socket.c

@@ -128,7 +128,18 @@ static ssize_t sock_sendpage(struct file *file, struct page *page,
 static ssize_t sock_splice_read(struct file *file, loff_t *ppos,
 				struct pipe_inode_info *pipe, size_t len,
 				unsigned int flags);
-static void sock_show_fdinfo(struct seq_file *m, struct file *f);
+
+#ifdef CONFIG_PROC_FS
+static void sock_show_fdinfo(struct seq_file *m, struct file *f)
+{
+	struct socket *sock = f->private_data;
+
+	if (sock->ops->show_fdinfo)
+		sock->ops->show_fdinfo(m, sock);
+}
+#else
+#define sock_show_fdinfo NULL
+#endif
 
 /*
  *	Socket files have a set of 'special' operations as well as the generic file ones. These don't appear
@@ -151,9 +162,7 @@ static const struct file_operations socket_file_ops = {
 	.sendpage =	sock_sendpage,
 	.splice_write = generic_splice_sendpage,
 	.splice_read =	sock_splice_read,
-#ifdef CONFIG_PROC_FS
 	.show_fdinfo =	sock_show_fdinfo,
-#endif
 };
 
 /*
@@ -997,14 +1006,6 @@ static ssize_t sock_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	return res;
 }
 
-static void sock_show_fdinfo(struct seq_file *m, struct file *f)
-{
-	struct socket *sock = f->private_data;
-
-	if (sock->ops->show_fdinfo)
-		sock->ops->show_fdinfo(m, sock);
-}
-
 /*
  * Atomic setting of ioctl hooks to avoid race
  * with module unload.