hyperv/vmbus: Allow driver to inject synchronous task into channel taskq.

Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D8208

hyperv/hn: Rework link status support.

This is the preamble for network device SR-IOV and
NDIS_STATUS_NETWORK_CHANGE handling.

Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D8209

hyperv/hn: Management parts always need suspend and resume.

Sponsored by:   Microsoft