[refactor] [semtech_adapter] increase buffer size
[refactor] [semtech_adapter] increase buffer size

We have to support the Semtech forwarder that can send datagrams of up to 4550 bytes.

mgranberry/ttn,jvanmalder/ttn,mgranberry/ttn,TheThingsNetwork/ttn,mgranberry/ttn,jvanmalder/ttn,TheThingsNetwork/ttn,TheThingsNetwork/ttn,LoRaWanSoFa/ttn,jvanmalder/ttn,LoRaWanSoFa/ttn