openvswitch: Remove egress_tun_info.

tun info is passed using skb-dst pointer. Now we have
converted all vports to netdev based implementation so
Now we can remove redundant pointer to tun-info from OVS_CB.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>