NTP broadcast client

An NTP broadcast client listens for NTP packets on a broadcast address. When the first packet is received, the client attempts to quantify the delay to the server, to better quantify the correct time from later broadcasts. This is accomplished by a series of brief interchanges where the client and server act as a regular (non-broadcast) NTP client and server. Once interchanges occur, the client has an idea of the network delay and thereafter can estimate the time based only on broadcast packets.