s3:vfs:gpfs: Remove all reading uses of stat_ex.vfs_private from vfs_gfs.

s3:vfs:gpfs: Remove all reading uses of stat_ex.vfs_private from vfs_gfs.

This was used as a cache for offline-info in the stat buffer.
But as the implementation of gpfs_is_offline() showed, this cache
does not always carry valid information when the stat itself is valid
(since at least one call goes to fstatat() directly, circumventing
 the vfs).

So the correct thing is to always call SMB_VFS_IS_OFFLINE()
when checking whether a file is offline. For the pread and pwrite
calls, we need to call IS_OFFLINE before the actual read
and check afterwards if the file was offline before (as a basis
whether to send notifications).

Signed-off-by: Michael Adam <obnox@samba.org>
Reviewed-by: Christof Schmitt <cs@samba.org>