vsock/test: add '--peer-port' input argument

Implement port for given CID as input argument instead of using
hardcoded value '1234'. This allows to run different test instances
on a single CID. Port argument is not required parameter and if it is
not set, then default value will be '1234' - thus we preserve previous
behaviour.

Signed-off-by: Arseniy Krasnov <avkrasnov@salutedevices.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://lore.kernel.org/r/20240123072750.4084181-1-avkrasnov@salutedevices.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>