Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

add ieee80211_isratevalid

Update PLCP<->rate mapping support:
o correct mapping of CCK rates to PLCP; was using nonstandard Ralink
values which just happened to also be used by Zydas (so went unnoticed)
o change ieee80211_plcp2rate api to take a phy type instead of a flag
that indicates ofdm/!ofdm
o update drivers to match (restore per-driver code to map rate->PLCP)

Reviewed by: sephe, weongyo, thompsa

Multi-bss (aka vap) support for 802.11 devices.

Note this includes changes to all drivers and moves some device firmware
loading to use firmware(9) and a separate module (e.g. ral). Also there
no longer are separate wlan_scan* modules; this functionality is now
bundled into the wlan module.

Supported by: Hobnob and Marvell
Reviewed by: many
Obtained from: Atheros (some bits)