hyperv/hn: Implement SIOC[SG]IFMEDIA support

Many applications and kernel modules (e.g. bridge) rely on the ifmedia
status report; give them what they want.

Submitted by: Dexuan Cui <decui microsoft com>
Reviewed by: Jun Su <junsu microsoftc com>, me, adrian
Modified by: me (minor)
Original differential: https://reviews.freebsd.org/D4611
Differential Revision: https://reviews.freebsd.org/D4852
Approved by: adrian (mentor)
Sponsored by: Microsoft OSTC