MFC 303603-303605,303764

MFC 303603-303605,303764

303603
    hyperv/vmbus: Remove the artificial entry limit of SG and PRP list.

    Just make sure that the total channel packet size does not exceed 1/2
    data size of the TX bufring.

    Sponsored by:   Microsoft
    Differential Revision:  https://reviews.freebsd.org/D7359

303604
    hyperv/storvsc: Set maxio to 128KB.

    Sponsored by:   Microsoft
    Differential Revision:  https://reviews.freebsd.org/D7360

303605
    hyperv/storvsc: Stringent PRP list assertions

    Sponsored by:   Microsoft
    Differential Revision:  https://reviews.freebsd.org/D7361

303764
    hyperv/vmbus: Only make sure the TX bufring will not be closed.

    KVP can write data, whose size is > 1/2 TX bufring size.

    Sponsored by:   Microsoft OSTC
    Differential Revision:  https://reviews.freebsd.org/D7414

git-svn-id: svn://svn.freebsd.org/base/stable/10@307137 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f