netfilter: synproxy: correct wscale option passing

netfilter: synproxy: correct wscale option passing

Timestamp are used to store additional syncookie parameters such as sack,
ecn, and wscale. The wscale value we need to encode is the client's
wscale, since we can't recover that later in the session. Next overwrite
the wscale option so the later synproxy_send_client_synack will send
the backend's wscale to the client.

Signed-off-by: Martin Topholm <mph@one.com>
Reviewed-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>