Merge branch 'fix-net-list-corruption' into net-cleanups
Restructuring of network output side.

Mostly refactoring the common code that was duplicated
between the different output types so that there aren't
many copies floating around.

This introduces "struct net_writer" to store the state of a
particular type of output service - buffers, time of last write,
connection count etc. prepareWrite() / completeWrite() give access
to the buffer and handle the actual writes and flushing when needed.

Heartbeat and time-based flushing move into a generic periodic-work
function.

Update the SBS output code to use the new infrastructure. This makes
a big different to CPU use when under load.
Merge branch 'net-cleanups'

Conflicts:
	dump1090.c