Another iteration on issue #193, fixes -B with some TCP tests.

When we do TCP tests and specify the socket buffer size, MSS, or
TCP no delay option, the iperf3 server destroys the socket it was
using to listen for the control connection and opens up a new
listening socket for the test's data connections.  This is (I think)
to make sure that the data connections all have the correct TCP
parameters.

When we re-create the listening socket, we also need to go through
the binding logic again (with all of the address family selectiion,
etc. goop).  The bug fixes that were a part of issue #193 need to
be ported to this code as well.

This problem only affects TCP tests, because for other protocols,
the listening socket for data cannot be the same listening sock as
for the control connection.

While here, add some comments so anybody trying to understand this
code will have an easier time.

Based on patch by:	@i2aaron