hyperv/hn: Don't allow NVS and NDIS version change upon reinitailization

NVS and NDIS version change would break too much assumption and static
configuration.

Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D7919

hyperv/hn: Save capabilities for later use.

And don't allow capability changes during reinitialization, which
breaks too much static configuration.

Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D7922

hyperv/hn: Don't allow MTU change, if it is not supported by the NVS.

Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D7923

hyperv/hn: Stringent RSS sysctl checks

- Don't change RNDIS RSS configuration for RSS key sysctl, if the
  interface is not capable of RSS yet.
- Don't change RSS indirect table (both cached one and RNDIS RSS
  configuration), if the interface is not capable of RSS yet.

Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D7924

hyperv/hn: Allow RSS capability flipping upon attach/reinit.

Sponsored by:   Microsoft
Differential Revision:  https://reviews.freebsd.org/D7927