Fix move handling of zvol devices out of txg sync thread

[anthoine.bourgeois_blade-group.com]

Summary

This revision fix the D7179 revision.

The patch is rebase on current and a queue applies all changes
in order between concurrent zfs rename and promote.

The queue protected by a mutex uses a condvar to wait for other
dataset changes to finish and keep order between calls.

PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=203864