Add in Packet Data FEC Scheme signalling in FIG0/14

[nickpiggott]

I've attempted to add in FIG0/14 to signal FEC Scheme on Packet Data channels.

Some points to be aware of:

• I'm not a C++ developer!
• FIG0_14.cpp, line 37 - the data field is a single byte, top 6 bits are SubChanID, bottom 2 bits are FEC type; is this how you organise the bits in the right order?
• FIG0_14.cpp, line 78 - there needs to be a test here if the packet channel is enhanced or not, but it looks like that attribute is only held on the file input, and not easily readable from the services configuration?
• FIG0_14.cpp, lines 101-106 - is this writing the entire FIC into the stack correctly? The usual preamble bytes for the service identifier followed by the 1 byte data field

[mpbraendli]

Thanks! I cherry-picked the commits onto the next branch (because I didn't want to take d508586) and I've added a flag so that FIG0/14 is inserted only for enhancedpacket subchannels.

The data field is thankfully only 1-byte, otherwise you have to care about endianness, and casting the buffer would probably also not be allowed (strict aliasing rule).

I verified with etisnoop, but it would be great if you could verify with another tool! Let me know if you can do that.