datapath: change type of UPCALL_PID attribute to NLA_UNSPEC

datapath: change type of UPCALL_PID attribute to NLA_UNSPEC

Upstream commit:
    commit ea8564c865299815095bebeb4b25bef474218e4c
    Author: Li RongQing <lirongqing@baidu.com>
    Date:   Tue Sep 24 19:11:52 2019 +0800

    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 6e237d099fac "(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: 5cd667b0a456 ("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>
Fixes: beb1c69a3 ("datapath: Allow each vport to have an array of 'port_id's.")
Cc: Li RongQing <lirongqing@baidu.com>
Signed-off-by: Greg Rose <gvrose8192@gmail.com>
Acked-by: Yi-Hung Wei <yihung.wei@gmail.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>