openvswitch: Remove flow member from struct ovs_skb_cb

The 'flow' memeber was chosen for removal because it's only used
in ovs_execute_actions() we can pass it as argument to this
function.

Signed-off-by: Lorand Jakab <lojakab@cisco.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>