Add NMEA2000 Speaker ID to translated output packets.

[brian-r-calder]

Although it shouldn't matter with a well designed and well functioning network, we sometimes see multiple talkers on a NMEA2000 network generating bad data. For example, alternating good and bad SystemTime packets:

[20296 days, 58430.399000000005 s., 148241 ms elapsed] SystemTime:  source = 15
[65535 days, -1000000000.0 s., 148626 ms elapsed] SystemTime:  source = 15
[20296 days, 58431.399000000005 s., 149240 ms elapsed] SystemTime:  source = 15
[65535 days, -1000000000.0 s., 149677 ms elapsed] SystemTime:  source = 15

Since there's no speaker information in the packets that we preserve to output (although there is in input), it's not possible to tell whether this is one speaker having a Very Bad Day, or two speakers, one of which is broken.

Therefore, it would be a good idea to hold on to the speaker ID information that's provided when we parse the NMEA2000 packet, and write it into the output file. This would, unfortunately, mean updating the packet definitions and generating a new serialiser (1.4).