introduce global var device clientId

include/globals.h

@@ -127,6 +127,7 @@ extern std::array<uint64_t, 0xff>::iterator it;
 extern std::array<uint64_t, 0xff> beacons;
 
 extern configData_t cfg;                       // current device configuration
+extern char clientId[20];                      // unique clientID
 extern char lmic_event_msg[LMIC_EVENTMSG_LEN]; // display buffer
 extern uint8_t volatile channel;               // wifi channel rotation counter
 extern uint8_t volatile rf_load;               // RF traffic indicator