iwmc3200wifi: Do not handle wifi command if the interface is not ready

When resetting or bringing the interface down, we should just reject any wifi
related command.

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