openvswitch: Suppress error messages on megaflow updates

With subfacets, we'd expect megaflow updates message to carry
the original micro flow. If not, EINVAL is returned and kernel
logs an error message.  Now that the user space subfacet layer is
removed, it is expected that flow updates can arrive with a
micro flow other than the original. Change the return code to
EEXIST and remove the kernel error log message.
Reported-by: Ben Pfaff <blp@nicira.com>
Signed-off-by: Andy Zhou <azhou@nicira.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>

net/openvswitch/datapath.c

@@ -860,11 +860,8 @@ static int ovs_flow_cmd_new_or_set(struct sk_buff *skb, struct genl_info *info)
 			goto err_unlock_ovs;
 
 		/* The unmasked key has to be the same for flow updates. */
-		error = -EINVAL;
-		if (!ovs_flow_cmp_unmasked_key(flow, &match)) {
-			OVS_NLERR("Flow modification message rejected, unmasked key does not match.\n");
+		if (!ovs_flow_cmp_unmasked_key(flow, &match))
 			goto err_unlock_ovs;
-		}
 
 		/* Update actions. */
 		old_acts = ovsl_dereference(flow->sf_acts);