mac80211 has 3 values for the antenna setup:
 0 - default
 1 - use antenna 1
 2 - use antenna 2

This means that rt2x00 should store the default value
from the EEPROM somwhere and use that when mac80211 indicates
that the antenna setup is 0.
This also implies that rt2x00 should no longer write the
hw->config.antenna_sel_* values based on the EEPROM input.

This also adds the basis in rt2x00lib for correct software
diversity handling. By default rt2x00lib will now configure
antenna B instead of hardware diversity.
Signed-off-by: NIvo van Doorn <IvDoorn@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>