net: simplify net_client_parse() error management

net: simplify net_client_parse() error management

All net_client_parse() callers exit in case of error.

Move exit(1) to net_client_parse() and remove error checking from
the callers.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>