This adds zd1211rw driver support for the softmac functionality I
added a while back. We now obey changes in basic rates, use short
preamble if it is available (but long if the AP says it's not),
and send self-CTS in the proper situations.

Locking fixed and improved by Ulrich Kunitz.
Signed-off-by: Daniel Drake <dsd@gentoo.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>