First stab at implementing better RSSI based connection status estimation, still needs some work and testing

src/drivers/drv_rc_input.h

@@ -89,6 +89,9 @@ struct rc_input_values {
 	/** number of channels actually being seen */
 	uint32_t		channel_count;
 
+	/** receive signal strength indicator (RSSI): < 0: Undefined, 0: no signal, 1000: full reception */
+	int32_t			rssi;
+
 	/** Input source */
 	enum RC_INPUT_SOURCE 	input_source;