[net80211] Initial full-offload scan support.
This is a very simple addition to the net80211 scan support.
It doesn't implement a replacement scan interface - it just disables
the pieces that we should disable to make this lifecycle a bit
more managable.
There's more work to come before full scan offload support is available
but it should be good enough for driver work.
* add a flag to say "full offload"
* don't do probe requests when scanning full-offload - firmware can do that
* don't do powersave transitions and buffering - firmware can do that
tested:
* iwm(4) - STA mode
* ath10k port (local, not in freebsd-head yet)
Reviewed by: avos
Differential Revision: https://reviews.freebsd.org/D8262
UnifiedSplitRaw
