[net80211] convert all of the WME use over to a temporary copy of WME info.

This removes the direct WME info access in the ieee80211com struct and instead
provides a method of fetching the data. Right now it's a no-op but eventually
it'll turn into a per-VAP method for drivers that support it (eg iwn, iwm,
upcoming ath10k work) as things like p2p support require this kind of behaviour.

Tested:

• ath(4), STA and AP mode

TODO:

• yes, this is slightly stack size-y, but it is an important first step to get drivers migrated over to a sensible WME API. A lot of per-phy things need to be converted to per-VAP before P2P, 11ac firmware, etc stuff shows up.