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)

net80211 rate control framework (net80211 ratectl).

This framework allows drivers to abstract the rate control algorithm and
just feed the framework with the usable parameters. The rate control
framework will now deal with passing the parameters to the selected
algorithm. Right now we have AMRR (the default) and RSSADAPT but there's
no way to select one with ifconfig, yet.
The objective is to have more rate control algorithms in the net80211
stack so all drivers[0] can use it. Ideally, we'll have the well-known
sample rate control algorithm in the net80211 at some point so all
drivers can use it (not just ath).

[0] all drivers that do rate control in software, that is.

Reviewed by: bschmidt, thompsa, weyongo
MFC after: 1 months

o uses bus accessor macros to read values from ivar so no more values
are referenced directly from ivar pointer. It's to do like what other
buses do. [1]
o changes exported prototypes. It doesn't use struct siba_* structures
anymore that instead of it it uses only device_t.
o removes duplicate code and debug messages.
o style(9)

Pointed out by: imp [1]

o adds sysctl variables to show device statistics.
o records RTS success/fail statistics.

Pointed by: imp

adds bwn(4) driver for supporting Broadcom BCM43xx chipsets.

o uses v4 firmware instead of v3. A port will be committed to create
the bwn firmware module.
o supports B/G and LP(low power) PHYs.
o supports 32 / 64 bits DMA operations.
o tested on big / little endian machines so should work on all
architectures.

It'd not connected to the build until the firmware port is committed.