vfs_gpfs: remove updating btime from stat VFS calls

vfs_gpfs: remove updating btime from stat VFS calls

This is now handled by the vfs_gpfs_(f)get_dos_attributes. Getting rid
of this in the stat VFS functions is a huge performance saver. perf
report found that in a kernel copy workload smbd was spending
considerable CPU time in vfs_gpfs_(f|l)stat -> gpfs_get_winattrs.

Most of the time the VFS stat caller is not interested in the btime. The
SMB frontend processing around btime is designed to fetch btime together
with DOS attributes via dos_mode() in all places that need these
attributes. That's the way it is implemented in the default VFS module
and that's what vfs_gpfs now does as well for performance reasons.

This makes vfs_gpfs_fstat a null op and I'm therefor removing it.

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Christof Schmitt <cs@samba.org>