Expose a counter to track RadioLib receive errors

This change counts when readData returns an err code other than RADIOLIB_ERR_NONE. In most cases this is going to be a CRC error. This counter is exposed in the `stats-packets` command, and in the repeater stats payload (4 additional bytes to the payload, which is now 56 bytes with this change. My incompetent robot claims the total payload size is 96 bytes (unverified but probably close).

examples/simple_repeater/MyMesh.cpp

@@ -226,7 +226,7 @@ int MyMesh::handleRequest(ClientInfo *sender, uint32_t sender_timestamp, uint8_t
     stats.n_direct_dups = ((SimpleMeshTables *)getTables())->getNumDirectDups();
     stats.n_flood_dups = ((SimpleMeshTables *)getTables())->getNumFloodDups();
     stats.total_rx_air_time_secs = getReceiveAirTime() / 1000;
-
+    stats.n_recv_errors = radio_driver.getPacketsRecvErrors();
     memcpy(&reply_data[4], &stats, sizeof(stats));
 
     return 4 + sizeof(stats); //  reply_len

examples/simple_repeater/MyMesh.h

@@ -54,6 +54,7 @@ struct RepeaterStats {
   int16_t  last_snr;   // x 4
   uint16_t n_direct_dups, n_flood_dups;
   uint32_t total_rx_air_time_secs;
+  uint32_t n_recv_errors;
 };
 
 #ifndef MAX_CLIENTS