fix: register Bluetooth and USB receivers using RECEIVER_EXPORTED flag

https://developer.android.com/develop/background-work/background-tasks/broadcasts#context-registered-receivers

Note from Step 4.:
"Some system broadcasts come from highly privileged apps, such as Bluetooth and telephony, that are part of the Android framework but do not run under the system's unique process ID (UID). To receive all system broadcasts, including broadcasts from highly privileged apps, flag your receiver with RECEIVER_EXPORTED."

app/src/main/java/com/geeksville/mesh/util/CompatExtensions.kt

@@ -41,7 +41,7 @@ fun PackageManager.getPackageInfoCompat(packageName: String, flags: Int = 0): Pa
 fun Context.registerReceiverCompat(
  receiver: BroadcastReceiver,
  filter: IntentFilter,
- flag: Int = ContextCompat.RECEIVER_NOT_EXPORTED,
+ flag: Int = ContextCompat.RECEIVER_EXPORTED,
 ) {
  ContextCompat.registerReceiver(this, receiver, filter, flag)
 }