syncookies: fix inclusion of tcp options in syn-ack

David Miller noticed that commit
33ad798c '(tcp: options clean up')
did not move the req->cookie_ts check.
This essentially disabled commit 4dfc2817
'[Syncookies]: Add support for TCP options via timestamps.'.

This restores the original logic.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>