vfs_gpfs: make sure get_quota does not return bogus values

vfs_gpfs: make sure get_quota does not return bogus values

add implementation of get_quota_fn to vfs_gpfs. The implemetation
returns ENOSYS for the case of user and group quota, to make sure
the default VFS does not accidentally succeed (and return wrong
values which would alter the disk-free calculation)

For other quota types the function calls the underlying VFS as
before.

Signed-off-by: Uri Simchoni <uri@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>