Document tor_ersatz_socketpair() and the functions it calls
The function comments in socketpair.c are missing or incomplete.
Maybe we should add function comments, using the tor_socketpair() comment as a starting point? https://github.com/torproject/tor/blob/701eaef980de4f7dbb5c31c4fee9b7e1e266d7a1/src/lib/net/socket.c#L450