UKERNEL: f_fsid is a struct on AIX

UKERNEL: f_fsid is a struct on AIX

The statvfs f_fsid member is a struct with two fields on AIX when
_ALL_SOURCE is defined (which we define to get various extensions). So
in the AIX case, use it as such a struct instead of a single integer.

Reviewed-on: http://gerrit.openafs.org/3260
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 7d6860c852296d96eac2785739bcfb9de76cd92d)

Change-Id: If8912f8cba8e12525f12f75cd53cf77bb7d4c547
Reviewed-on: http://gerrit.openafs.org/3510
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>