iwlwifi: don't return -ERFKILL if SEND_IF_RFKILL is set

When CMD_SEND_IN_RFKILL is set, it is perfectly legitimate
to send a host command while RFKILL is asserted. In this
case, the host command sending functions should return 0
even if RFKILL is asserted.

Signed-off-by: Eran Harary <eran.harary@intel.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>