rt2x00: Fix regression for rt2500pci

Since commit:
     commit f1aa4c54
     Author: Ivo van Doorn <ivdoorn@gmail.com>
     Date:   Tue Jun 29 21:38:55 2010 +0200

     rt2x00: Write the BSSID to register when interface is added

mananged mode in rt2500pci was broken, due to intf->bssid containing
random data rather then the expected 00:00:00:00:00:00

This is corrected by sending the BSSID to rt2x00lib_config_intf
only in AP mode where the bssid is set to a valid value.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Acked-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>