[NETFILTER] {ip,nf}_conntrack TCP: Accept SYN+PUSH like SYN

Some devices (e.g. Qlogic iSCSI HBA hardware like QLA4010 up to firmware
3.0.0.4) initiates TCP with SYN and PUSH flags set.

The Linux TCP/IP stack deals fine with that, but the connection tracking
code doesn't.

This patch alters TCP connection tracking to accept SYN+PUSH as a valid
flag combination.

Signed-off-by: Vlad Drukker <vlad@storewiz.com>
Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>