Add switch logic for high latency telemetry in commander

Switch to the high latency telemetry, if available, if every low latency link is lost. Switch back if any low latency link is regained. Only indicate that all links are lost if all high and low latency links are lost. Allow different timeouts for high and low latency links.

src/drivers/telemetry/iridiumsbd/IridiumSBD.h

@@ -86,7 +86,7 @@ extern "C" __EXPORT int iridiumsbd_main(int argc, char *argv[]);
 #define SATCOM_TX_BUF_LEN				340		// TX buffer size - maximum for a SBD MO message is 340, but billed per 50
 #define SATCOM_RX_MSG_BUF_LEN			270		// RX buffer size for MT messages
 #define SATCOM_RX_COMMAND_BUF_LEN		50		// RX buffer size for other commands
-#define SATCOM_SIGNAL_REFRESH_DELAY		20000000 // update signal quality every 5s
+#define SATCOM_SIGNAL_REFRESH_DELAY		20000000 // update signal quality every 20s
 
 class IridiumSBD : public device::CDev
 {