Add sub band channel selection for AU915

Also see https://github.com/mcci-catena/arduino-lmic/commits/master/examples/ttn-abp/ttn-abp.ino

src/loraconf_abp.cpp

@@ -39,8 +39,8 @@ void setABPParameters() {
     // devices' ping slots. LMIC does not have an easy way to define set this
     // frequency and support for class B is spotty and untested, so this
     // frequency is not configured here.
-    #elif defined(CFG_us915)
-    // NA-US channels 0-71 are configured automatically
+    #elif defined(CFG_us915) || defined(CFG_au915)
+    // NA-US and AU channels 0-71 are configured automatically
     // but only one group of 8 should (a subband) should be active
     // TTN recommends the second sub band, 1 in a zero based count.
     // https://github.com/TheThingsNetwork/gateway-conf/blob/master/US-global_conf.json