Enable Telemetry on DumbRC receivers (#1111)

Tested with X6FGv1.1, X6FP, X6DC(G)v1.1

I also tested with multiple X6F receivers and some gave RSSI Telem and some gave nothing.
2 of them had the same PCB as the X6FP and neither gave telemetry.
I had a third with the same PCB with the X6FP which did give RSSI
and of my two with an older PCB one gives RSSI telem and the other does not.

Of the receivers I tried only one set packet_in[6] to match the TX packet[1] and it was the
oldest receiver of the ones I own.

Author: Jonimoose

Multiprotocol/RadioLink_cc2500.ino

@@ -232,7 +232,7 @@ static void __attribute__((unused)) RLINK_send_packet()
 			packet[1] |= 0x21;					//air 0x21 on dump but it looks to support telemetry at least RSSI
 			break;
 		case RLINK_DUMBORC:
-			packet[1]  = 0x00;					//always 0x00 on dump
+			packet[1] |= 0x01;					//always 0x00 on dump but does appear to support telemtry on newer transmitters
 			break;
 	}
 
@@ -384,8 +384,9 @@ uint16_t RLINK_callback()
 					debug("Telem:");
 				#endif
 				CC2500_ReadData(packet_in, len);
-				if(packet_in[0]==RLINK_RX_PACKET_LEN && (packet_in[len-1] & 0x80) && memcmp(&packet[2],rx_tx_addr,RLINK_TX_ID_LEN)==0 && packet_in[6]==packet[1])
+				if(packet_in[0]==RLINK_RX_PACKET_LEN && (packet_in[len-1] & 0x80) && memcmp(&packet[2],rx_tx_addr,RLINK_TX_ID_LEN)==0 && (packet_in[6]==packet[1] || sub_protocol == RLINK_DUMBORC))
 				{//Correct telemetry received: length, CRC, ID and type
+				 //packet_in[6] is 0x00 on almost all DumboRC RX so assume it is always valid
 					#ifdef RLINK_DEBUG_TELEM
 						for(uint8_t i=0;i<len;i++)
 							debug(" %02X",packet_in[i]);