preliminary implementation of "smart_nopush"

preliminary implementation of "smart_nopush"

It only supports TCP_CORK under Linux right now.

We use a very basic strategy to use TCP_CORK semantics optimally
in most TCP servers:  On corked sockets, we will uncork on recv()
if there was a previous send().  Otherwise we do not fiddle
with TCP_CORK at all.

Under Linux, we can rely on TCP_CORK being inherited in an
accept()-ed client socket so we can avoid syscalls for each
accept()-ed client if we already know the accept() socket corks.

This module does NOTHING for client TCP sockets, we only deal
with accept()-ed sockets right now.