md: round-trip the MUSTDEALLOC and RESERVE options

If those options are requested when the device is created, ensure that
they will be reported by MDIOCQUERY.

Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1270

(cherry picked from commit 9d449caddd4f442ba4ebfd2edafa1aef4fcba4c8)