MFC r312689, r312690

MFC r312689, r312690

Approved by:	sephe (mentor)

r312689
    hyperv/hn: add a sysctl name for the VF interface

    This makes it easier for the userland script to find the releated
    VF interface.

    Reviewed by:	sephe
    Approved by:	sephe (mentor)
    Sponsored by:	Microsoft
    Differential Revision:	https://reviews.freebsd.org/D9101

r312690
    hyperv/hn: add devctl_notify for VF_UP/DOWN events

    Reviewed by:	sephe
    Approved by:	sephe (mentor)
    Sponsored by:	Microsoft
    Differential Revision:	https://reviews.freebsd.org/D9102

git-svn-id: svn://svn.freebsd.org/base/stable/10@314124 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f