[PATCH] ipw2200: Set a meaningful silence threshold value

Set a meaningful silence threshold value (replacing our previous "0"
default), which gets rid of the gratuitous "Link deterioration"
notifications that we've been receiving from firmware.  This
notification feature tells the driver information to help it determine
when to pre-emptively restart the firmware/ucode in anticipation of
firmware errors!  But since setting this new threshold, I haven't seen
any such notifications.  At least it keeps the logs a little less busy.

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>