openvswitch: Fix ovs_dp_cmd_msg_size()

commit 43d4be9cb5 (openvswitch: Allow user space
to announce ability to accept unaligned Netlink messages) introduced
OVS_DP_ATTR_USER_FEATURES netlink attribute in datapath responses,
but the attribute size was not taken into account in ovs_dp_cmd_msg_size().

Signed-off-by: Daniele Di Proietto <daniele.di.proietto@gmail.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>

net/openvswitch/datapath.c

@@ -1087,6 +1087,7 @@ static size_t ovs_dp_cmd_msg_size(void)
 	msgsize += nla_total_size(IFNAMSIZ);
 	msgsize += nla_total_size(sizeof(struct ovs_dp_stats));
 	msgsize += nla_total_size(sizeof(struct ovs_dp_megaflow_stats));
+	msgsize += nla_total_size(sizeof(u32)); /* OVS_DP_ATTR_USER_FEATURES */
 
 	return msgsize;
 }