p2p/discover: bump packet timeouts to 500ms

p2p/discover/udp.go

@@ -31,8 +31,8 @@ var (
 
 // Timeouts
 const (
-	respTimeout = 300 * time.Millisecond
-	sendTimeout = 300 * time.Millisecond
+	respTimeout = 500 * time.Millisecond
+	sendTimeout = 500 * time.Millisecond
 	expiration  = 20 * time.Second
 
 	refreshInterval = 1 * time.Hour