cap exponential backoff at 300s (10 attempts)

src/main/java/eu/siacs/conversations/xmpp/XmppConnection.java

@@ -1422,7 +1422,7 @@ public class XmppConnection implements Runnable {
 	}
 
 	public int getTimeToNextAttempt() {
-		final int interval = (int) (25 * Math.pow(1.5, attempt));
+		final int interval = Math.min((int) (25 * Math.pow(1.3, attempt)), 300);
 		final int secondsSinceLast = (int) ((SystemClock.elapsedRealtime() - this.lastConnect) / 1000);
 		return interval - secondsSinceLast;
 	}