hyperv/vmbus: Event handling code refactor.

- Use taskqueue instead of swi for event handling.
- Scan the interrupt flags in filter
- Disable ringbuffer interrupt mask in filter to ensure no unnecessary
  interrupts.

Submitted by:               Jun Su <junsu microsoft com>
Reviewed by:                adrian, sephe, Dexuan <decui microsoft com>
Approved by:                adrian (mentor)
MFC after:          2 weeks
Sponsored by:               Microsoft OSTC
Differential Revision:      https://reviews.freebsd.org/D4920