When an active socket has data available, increment the io and read
counters, and schedule the ioworker.

Implement the read function by reading from the socket, writing the data
to the data ring.

Set in_error on error.
Signed-off-by: NStefano Stabellini <stefano@aporeto.com>
Reviewed-by: NJuergen Gross <jgross@suse.com>
CC: boris.ostrovsky@oracle.com
CC: jgross@suse.com
Signed-off-by: NBoris Ostrovsky <boris.ostrovsky@oracle.com>