headers_check fix: linux/elf.h

fix the following 'make headers_check' warnings:

  usr/include/linux/elf.h:379: extern's make no sense in userspace
  usr/include/linux/elf.h:387: extern's make no sense in userspace
  usr/include/linux/elf.h:401: extern's make no sense in userspace
  usr/include/linux/elf.h:402: extern's make no sense in userspace
Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>

include/linux/elf.h

@@ -377,6 +377,7 @@ typedef struct elf64_note {
   Elf64_Word n_type;	/* Content type */
 } Elf64_Nhdr;
 
+#ifdef __KERNEL__
 #if ELF_CLASS == ELFCLASS32
 
 extern Elf32_Dyn _DYNAMIC [];
@@ -404,5 +405,5 @@ static inline int elf_coredump_extra_notes_write(struct file *file,
 extern int elf_coredump_extra_notes_size(void);
 extern int elf_coredump_extra_notes_write(struct file *file, loff_t *foffset);
 #endif
-
+#endif /* __KERNEL__ */
 #endif /* _LINUX_ELF_H */