hyperv/hn: Use IFQ_DRV_PREPEND instead of IF_PREPEND

IF_PREPEND promises out-of-order packet sending when the TX desc list
is depleted. It was overlooked and copied blindly when the transmission
path was partially rewritten.

MFC after: 1 week
Sponsored by: Microsoft OSTC
Differential Revision: https://reviews.freebsd.org/D5386