[x] Make UDP packet formats uniform (everything should be an ad_latlng_packet_t; lat & lng values can be zero when not expecting them)
[x] Incorporate payload state data into heartbeat packets (either split data byte of packet into payload ID and payload state, or just send another byte in the packet representing the payload state)
[x] reevalute whether or not we still need certain acks depending on how much info is encoded in heartbeat
ad_latlng_packet_t; lat & lng values can be zero when not expecting them)