MFC 307952,307953,308278

MFC 307952,307953,308278

307952
    hyperv/vmbus: Add missing white space.

    Submitted by:   QianYue You <t-youqi microsoft com>
    Sponsored by:   Microsoft

307953
    hyperv/vmbus: Implement vmbus_chan_printf.

    And use it for vmbus channel logging, which can log the channel
    owner's name properly, instead of vmbus0.

    Submitted by:   QianYue You <t-youqi microsoft com>
    Sponsored by:   Microsoft

308278
    hyperv/vmbus: Reset ch_dev, once the child is deleted.

    So it will not be mis-used later on, e.g. in vmbus_chan_printf().

    Submitted by:   dexuan
    Reported by:    dexuan
    Sponsored by:   Microsoft

git-svn-id: svn://svn.freebsd.org/base/stable/10@308501 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f