[PATCH] ipw2200: Filter unsupported channels out in ad-hoc mode

Currently iwlist ethX freq[uency]/channel lists all the channels the card
supported for the current region, which includes some channels can only
be used in infrastructure mode. This patch filters these channels out if
the card is currently in ad-hoc mode.

Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>