smbd:close: only remove kernel share modes if they had been taken at open

smbd:close: only remove kernel share modes if they had been taken at open

This avoids errors due to 'not implemented' for SMB_VFS_KERNEL_FLOCK
on some file systems like glusterfs (with the vfs module). The only
other code path where SMB_VFS_KERNEL_FLOCK is called, is already protected.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11919

Signed-off-by: Michael Adam <obnox@samba.org>
Reviewed-by: Christian Ambach <ambi@samba.org>
Autobuild-User(master): Christian Ambach <ambi@samba.org>
Autobuild-Date(master): Thu May 19 02:34:36 CEST 2016 on sn-devel-144