libertas_tf: main.c, data paths and mac80211 handlers

This patch contains most of the libertastf driver, just lacking command helper
functions and usb specific functions. Currently, monitor, managed, ap and mesh
interfaces are supported. Even though this driver supports the same hardware as
the "libertas" driver, it uses a different (thin) firmware, that makes it
suitable for a mac80211 driver.

Signed-off-by: Luis Carlos Cobo <luisca@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>