hyperv/hn: Add multiple channel support, a.k.a. vRSS

Each channel contains one RX ring and one TX ring. And we
try to distribute the channels to different evenly.

Note: Currently we don't have enough information to extract
the RSS type and RSS hash value from the received packets.

This greatly improves the TX/RX performance for 8 virtual CPU
Hyper-V over 10Ge: it can max out 10Ge for TCP when multiple
RX/TX rings are enabled.

This almost doubles the TX/RX performance for locally connected
Hyper-Vs: was 6Gbps w/ 128 TCP streams, now 11Gbps w/ multiple
RX/TX rings enabled.

It is not enabled by default; it will be switched on after more
tests.

Collaborated with: Hongjiang Zhang <honzhan microsoft com>
MFC after: 2 week
Sponsored by: Microsoft OSTC