openvswitch: change type of UPCALL_PID attribute to NLA_UNSPEC

userspace openvswitch patch "(dpif-linux: Implement the API
functions to allow multiple handler threads read upcall)"
changes its type from U32 to UNSPEC, but leave the kernel
unchanged

and after kernel 6e237d099f "(netlink: Relax attr validation
for fixed length types)", this bug is exposed by the below
warning

	[   57.215841] netlink: 'ovs-vswitchd': attribute type 5 has an invalid length.

Fixes: 5cd667b0a4 ("openvswitch: Allow each vport to have an array of 'port_id's")
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/openvswitch/datapath.c

@@ -2294,7 +2294,7 @@ static const struct nla_policy vport_policy[OVS_VPORT_ATTR_MAX + 1] = {
 	[OVS_VPORT_ATTR_STATS] = { .len = sizeof(struct ovs_vport_stats) },
 	[OVS_VPORT_ATTR_PORT_NO] = { .type = NLA_U32 },
 	[OVS_VPORT_ATTR_TYPE] = { .type = NLA_U32 },
-	[OVS_VPORT_ATTR_UPCALL_PID] = { .type = NLA_U32 },
+	[OVS_VPORT_ATTR_UPCALL_PID] = { .type = NLA_UNSPEC },
 	[OVS_VPORT_ATTR_OPTIONS] = { .type = NLA_NESTED },
 	[OVS_VPORT_ATTR_IFINDEX] = { .type = NLA_U32 },
 	[OVS_VPORT_ATTR_NETNSID] = { .type = NLA_S32 },