try to recycle "snap" vnodes as soon as possible

Those vnodes should not linger. "Stale" nodes may get out of
synchronization with actual snapshots. For example if we destroy a
snapshot and create a new one with the same name. Or when we rename a
snapshot.

While there fix the argument type for zfsctl_snapshot_reclaim().
Also, its original argument can be passed to gfs_vop_reclaim() directly.

Bug 209093 could be related although I have not specifically verified
that. Referencing just in case.

PR: 209093
MFC after: 5 weeks