userfaultfd: selftest: headers fixup

userfaultfd: selftest: headers fixup

Orabug: 21685254

Depend on "make headers_install" to create proper headers to include and
provide syscall numbers.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Thierry Reding <treding@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 67f6a029b2ccf3399783a0ff2f812666f290d94f)
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Dhaval Giani <dhaval.giani@oracle.com>
Conflicts:
	tools/testing/selftests/vm/userfaultfd.c

Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>