openvswitch: Fix tracking of flags seen in TCP flows.

openvswitch: Fix tracking of flags seen in TCP flows.

Flow statistics need to take into account the TCP flags from the packet
currently being processed (in 'key'), not the TCP flags matched by the
flow found in the kernel flow table (in 'flow').

This bug made the Open vSwitch userspace fin_timeout action have no effect
in many cases.
This bug is introduced by commit 014cf1f44d189cef583 (openvswitch: Use
TCP flags in the flow key for stats.)

Reported-by: Len Gao <leng@vmware.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>