headers_check fix: linux/socket.h

fix the following 'make headers_check' warning:

  usr/include/linux/socket.h:29: extern's make no sense in userspace
Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>

include/linux/socket.h

@@ -24,10 +24,12 @@ struct __kernel_sockaddr_storage {
 #include <linux/types.h>		/* pid_t			*/
 #include <linux/compiler.h>		/* __user			*/
 
-#ifdef CONFIG_PROC_FS
+#ifdef __KERNEL__
+# ifdef CONFIG_PROC_FS
 struct seq_file;
 extern void socket_seq_show(struct seq_file *seq);
-#endif
+# endif
+#endif /* __KERNEL__ */
 
 typedef unsigned short	sa_family_t;