net: Destroy when not readable and not writable

This is only relevant for CentOS 6.3 using kernel version 2.6.32.

On other linuxes and darwin, the `read` call gets an ECONNRESET in that
case.  On sunos, the `write` call fails with EPIPE.

However, old CentOS will occasionally send an EOF instead of a
ECONNRESET or EPIPE when the client has been destroyed abruptly.

Make sure we don't keep trying to write or read more in that case.

Fixes #5504

However, there is still the question of what libuv should do when it
gets an EOF.  Apparently in this case, it will continue trying to read,
which is almost certainly the wrong thing to do.

That should be fixed in libuv, even though this works around the issue.