openvswitch: Set event bit after initializing labels.

Connlabels are included in conntrack netlink event messages only if
the IPCT_LABEL bit is set in the event cache (see
ctnetlink_conntrack_event()).  Set it after initializing labels for a
new connection.

Found upon further system testing, where it was noticed that labels
were missing from the conntrack events.

Fixes: 193e3096 ("openvswitch: Do not trigger events for unconfirmed connections.")
Signed-off-by: Jarno Rajahalme <jarno@ovn.org>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>