I'm seeing a problem on s390 with the new "SOCK_STREAM transport change
null-ptr-deref" test. Here is how it appears to happen:
test_stream_transport_change_client() spins for 2s and sends 70K+
CONTROL_CONTINUE messages to the "control" socket.
test_stream_transport_change_server() spins calling accept() because it
keeps receiving CONTROL_CONTINUE.
When the client exits, the server has received just under 1K of those
70K CONTROL_CONTINUE, so it calls accept() again but the client has
exited, so accept() never returns and the server never exits.
