BootCompletedReceiver: Enforce receiving the correct broadcast

This satisfies an Android security lint.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

app/src/main/java/com/wireguard/android/BootCompletedReceiver.java

@@ -8,6 +8,8 @@ public class BootCompletedReceiver extends BroadcastReceiver {
 
     @Override
     public void onReceive(Context context, Intent intent) {
+        if (!intent.getAction().equals(Intent.ACTION_BOOT_COMPLETED))
+            return;
         Intent startServiceIntent = new Intent(context, ProfileService.class);
         context.startService(startServiceIntent);
     }