[PATCH] Simple support for networked IO

Adds a new ioengine, net. Use with ioengine=net, it supports only strict
reading or writing (no mixed reads/writes) to/from a single host.
The filename given must contain the host and port to connect to (or
listen from).

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>