fix lint UnsafeProtectedBroadcastReceiver

Android won't protect us from other apps sending other Intents to these
receivers, so at least check that the action string matches what its
looking for.  This is based on a lint recommendation.

app/build.gradle

@@ -203,7 +203,7 @@ android {
         // to make CI fail on errors until this is fixed https://github.com/rtyley/spongycastle/issues/7
         warning 'InvalidPackage'
 
-        error 'AppCompatMethod', 'NestedScrolling', 'StringFormatCount'
+        error 'AppCompatMethod', 'NestedScrolling', 'StringFormatCount', 'UnsafeProtectedBroadcastReceiver'
     }
 
     packagingOptions {

app/src/main/java/org/fdroid/fdroid/receiver/StartupReceiver.java

@@ -23,12 +23,18 @@ import android.content.Context;
 import android.content.Intent;
 
 import org.fdroid.fdroid.UpdateService;
+import org.fdroid.fdroid.Utils;
 
 public class StartupReceiver extends BroadcastReceiver {
+    private static final String TAG = "StartupReceiver";
 
     @Override
     public void onReceive(Context ctx, Intent intent) {
-        UpdateService.schedule(ctx);
+        if (Intent.ACTION_BOOT_COMPLETED.equals(intent.getAction())) {
+            UpdateService.schedule(ctx);
+        } else {
+            Utils.debugLog(TAG, "received unsupported Intent " + intent);
+        }
     }
 
 }

app/src/main/java/org/fdroid/fdroid/receiver/WifiStateChangeReceiver.java

@@ -4,14 +4,21 @@ import android.content.BroadcastReceiver;
 import android.content.ComponentName;
 import android.content.Context;
 import android.content.Intent;
+import android.net.wifi.WifiManager;
 
+import org.fdroid.fdroid.Utils;
 import org.fdroid.fdroid.net.WifiStateChangeService;
 
 public class WifiStateChangeReceiver extends BroadcastReceiver {
+    private static final String TAG = "WifiStateChangeReceiver";
 
     @Override
     public void onReceive(Context context, Intent intent) {
-        intent.setComponent(new ComponentName(context, WifiStateChangeService.class));
-        context.startService(intent);
+        if (WifiManager.NETWORK_STATE_CHANGED_ACTION.equals(intent.getAction())) {
+            intent.setComponent(new ComponentName(context, WifiStateChangeService.class));
+            context.startService(intent);
+        } else {
+            Utils.debugLog(TAG, "received unsupported Intent: " + intent);
+        }
     }
 }