syncookies: avoid unneeded tcp header flag double check

caller: if (!th->rst && !th->syn && th->ack)
callee: if (!th->ack)

make the caller only check for !syn (common for 3whs), and move
the !rst / ack test to the callee.

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

diff --cc net/ipv4/syncookies.c
Simple merge

diff --cc net/ipv4/tcp_ipv4.c
Simple merge

diff --cc net/ipv6/syncookies.c
Simple merge

diff --cc net/ipv6/tcp_ipv6.c
Simple merge