Improve Hyper-V support.

vmbus(4):
- Added support for multichannel.

hvn(4):
- Added support for multichannel.
- Added support for change MTU.
- Added support for TX aggregation.
- Improve VLA

Improve Hyper-V support.

vmbus(4):
- Added support for multichannel.

hvn(4):
- Added support for multichannel.
- Added support for change MTU.
- Added support for TX aggregation.
- Improve VLAN support.
- Improve checksum offload support.

show more ...

Added drivers for Hyper-V Synthetic Keyboard and Video device.

Added Microsoft Hyper-V support. It ported from OpenBSD and FreeBSD.

graphical console is not work on Gen.2 VM yet. To use the serial console,
enter "consdev com,0x3f8,115200" on efiboot.