Increase MTU for Linux GATT server

[pippolo84]

I'm running the server example on an ARM embedded system equipped with Linux and to test it I sent some data through Renesas GATTBrowser on an Android device.
The example has been slightly modified to print the received data (below the interesting part of the code):

func f(req ble.Request, rsp ble.ResponseWriter) {
	fmt.Println(string(req.Data()))
}

func main() {
	// ...
	testSvc := ble.NewService(lib.TestSvcUUID)
	testSvc.AddCharacteristic(lib.NewCountChar())
	ch := lib.NewEchoChar()
	ch.HandleWrite(ble.WriteHandlerFunc(f))
	testSvc.AddCharacteristic(ch)
	// ...

I saw that the payload is always truncated to 20 bytes, no matter how many bytes I send from the Android device.
Is there a way to change the MTU or maybe enable some sort of chunking?

Thank you in advance!