GCS_MAVLink: allow use of RC_CHANNELS message on AVR too

can have up to 11 channels

libraries/GCS_MAVLink/GCS_Common.cpp

@@ -1015,7 +1015,6 @@ void GCS_MAVLINK::send_radio_in(uint8_t receiver_rssi)
         values[7],
         receiver_rssi);
 
-#if HAL_CPU_CLASS > HAL_CPU_CLASS_16
     if (hal.rcin->num_channels() > 8 && 
         comm_get_txspace(chan) >= MAVLINK_MSG_ID_RC_CHANNELS_LEN + MAVLINK_NUM_NON_PAYLOAD_BYTES) {
         mavlink_msg_rc_channels_send(
@@ -1042,7 +1041,6 @@ void GCS_MAVLINK::send_radio_in(uint8_t receiver_rssi)
             hal.rcin->read(CH_18),
             receiver_rssi);        
     }
-#endif
 }
 
 void GCS_MAVLINK::send_raw_imu(const AP_InertialSensor &ins, const Compass &compass)