reiserfs_xattr.h: add linux/reiserfs_xattr.h to UAPI compile-test coverage

linux/reiserfs_xattr.h is currently excluded from the UAPI compile-test
because of the error like follows:

HDRTEST usr/include/linux/reiserfs_xattr.h
In file included from <command-line>:
./usr/include/linux/reiserfs_xattr.h:22:9: error: unknown type name ‘size_t’
22 | size_t length;
| ^~~~~~

The error can be fixed by replacing size_t with __kernel_size_t.

Then, remove the no-header-test entry from user/include/Makefile.

Signed-off-by: Masahiro Yamada <[e-mail]>
Reviewed-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>

include/uapi/linux/reiserfs_xattr.h

···
 struct reiserfs_security_handle {
 	const char *name;
 	void *value;
-	size_t length;
+	__kernel_size_t length;
 };
 
 #endif  /*  _LINUX_REISERFS_XATTR_H  */

usr/include/Makefile

···
 no-header-test += linux/omapfb.h
 no-header-test += linux/patchkey.h
 no-header-test += linux/phonet.h
-no-header-test += linux/reiserfs_xattr.h
 no-header-test += linux/sctp.h
 no-header-test += linux/sysctl.h
 no-header-test += linux/usb/audio.h