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