openvswitch: Only set mark and labels with a commit flag.

Only set conntrack mark or labels when the commit flag is specified.
This makes sure we can not set them before the connection has been
persisted, as in that case the mark and labels would be lost in an
event of an userspace upcall.

OVS userspace already requires the commit flag to accept setting
ct_mark and/or ct_labels.  Validate for this in the kernel API.

Signed-off-by: Jarno Rajahalme <jarno@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>