MFC 294886

MFC 294886

    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

git-svn-id: svn://svn.freebsd.org/base/stable/10@301854 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f