check ADVICE of fadvise64_64 even if get_xip_page is given

I've written some test programs in ltp project.  During writing I met an
problem which I cannot solve in user land.  So I wrote a patch for linux
kernel.  Please, include this patch if acceptable.

The test program tests the 4th parameter of fadvise64_64:

    long sys_fadvise64_64(int fd, loff_t offset, loff_t len, int advice);

My test case calls fadvise64_64 with invalid advice value and checks errno is
set to EINVAL.  About the advice parameter man page says:

    ...
    Permissible values for advice include:

	   POSIX_FADV_NORMAL
                  ...
	   POSIX_FADV_SEQUENTIAL
                  ...
	   POSIX_FADV_RANDOM
		  ...
	   POSIX_FADV_NOREUSE
                  ...
	   POSIX_FADV_WILLNEED
                  ...
	   POSIX_FADV_DONTNEED
		  ...
    ERRORS
           ...
	   EINVAL An invalid value was specified for advice.

However, I got a bug report that the system call invocations
in my test case returned 0 unexpectedly.

I've inspec...