MFC 296022,296024,296076

MFC 296022,296024,296076

296022
    hyperv/hn: Implement ifnet.if_transmit method

    It will be turned on by default later.

    MFC after:  1 week
    Sponsored by:       Microsoft OSTC
    Differential Revision:      https://reviews.freebsd.org/D5415

296024
    hyperv/hn: Hold the TX ring lock then drain TX desc buf_ring

    Reported by:        Hongxiong Xian <v-hoxian microsoft com>
    MFC after:  1 week
    Sponsored by:       Microsoft OSTC

296076
    hyperv: Use atomic_fetchadd_int to get GPADL id.

    Reviewed by:        Hongjiang Zhang <honzhan microsoft com>
    MFC after:  1 week
    Sponsored by:       Microsoft OSTC
    Differential Revision:      https://reviews.freebsd.org/D5439

git-svn-id: svn://svn.freebsd.org/base/stable/10@301911 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f