Don't attempt to manually set the channel in infrastructure mode, the
  firmware doesn't like that much.  Also don't attempt to override the
  firmware's default channel number for IBSS mode (I believe default
  channel can vary by regulatory domain).
Signed-off-by: NDavid Gibson <hermes@gibson.dropbear.id.au>
Signed-off-by: NJeff Garzik <jgarzik@pobox.com>