Spawn multiple threads and run system calls on TCP socket in parallel.

Setup TCP connections on localhost and run system calls connect(2),
accept(2), send(2), recv(2), and close(2) in parallel.  In addition
stress test for socket splicing, unsplice, max length and idle
timeout can run.  Alternatively to close(2) the tcp drop sysctl(2)
can be used.  The successful operations are counted.