Reliabilty of the Will Setup Exchange on Connect

This was highlighted by Davide Lenzarini in asking the question about the timeouts involved in the connect procedure with will setup. This involves a 6 packet exchange - when should the client timeout when waiting for one of those packets from the Gateway?

This then morphed into the question of why have separate packets to set the will at all, why not have the will message in the connect packet? The original reasons for this were twofold:

1. The length of each packet is minimized because of the reduced MTU or max packet size generally supplied by transports used by MQTT-SN
2. MQTT-SN was originally designed to have only one length field per packet - the overall length. This meant that there could be only one variable length field per packet. We now have deviated from that in the publish packet, so it could be done in the connect packet too.