[PATCH] ipw2200: Enables the "slow diversity" algorithm

This forces one antenna or the other, if the background noise is
significantly quieter in one than the other. It favors the quieter
antenna, and won't kick in unless the difference is significant.

Signed-off-by: Cahill, Ben M <ben.m.cahill@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>