oxenstored: save remote evtchn port, not local port

oxenstored: save remote evtchn port, not local port

Previously, Domain.dump output the number of the local port
corresponding to each domain's event-channel. However, when oxenstored
exits, it closes /dev/xen/evtchn which causes the kernel to close the
local port (evtchn_release), so this port is no longer useful.

Instead, store the remote port. This can be used to reconnect the
event-channel by binding the original remote port to a fresh local port.

Indeed, the logic for parsing the stored state already expects a remote
port as it passes the parsed port number to Domain.make (via
Domains.create), which takes a remote port.

Signed-off-by: Jonathan Davies <jonathan.davies@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Christian Lindig <christian.lindig@citrix.com>
Release-acked-by: Julien Grall <julien.grall@arm.com>