[OPTIM] stream_sock: don't shutdown(write) when the socket is in error

[OPTIM] stream_sock: don't shutdown(write) when the socket is in error

We get a lot of those, especially with web crawlers :

recv(2, 0x810b610, 7000, 0)             = -1 ECONNRESET (Connection reset by peer)
shutdown(2, 1 /* send */)               = -1 ENOTCONN (Transport endpoint is not connected)
close(2)                                = 0

There's no need to perform the shutdown() here, the socket is already
in error so it is down.