FreeBSD: Lock vnode in zfs_ioctl()

Previously vnode was not locked there, unlike Linux. It required
locking it in vn_flush_cached_data(), which recursed on the lock
if called from zfs_clone_range(), having the vnode locked.

Reviewed-by: Alan Somers <asomers@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored by: iXsystems, Inc.
Closes #16789
Closes #16796