Staging: dst: network state machine.

Each DST device contains of two nodes: local and remote (called also as export node).
This patch contains local node processing engine: network state storage,
socket processing loops and state machine, socket polling machinery, reconnection
logic, send/receive basic helpers, related IO commands and so on.

Signed-off-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>