datapath: Add hash info to upcall.

datapath: Add hash info to upcall.

This patch backports below upstream patches, and add __skb_set_hash
to compat for older kernels.

commit b5ab1f1be6180a2e975eede18731804b5164a05d
Author: Jakub Kicinski <kuba@kernel.org>
Date:   Mon Mar 2 21:05:18 2020 -0800

    openvswitch: add missing attribute validation for hash

    Add missing attribute validation for OVS_PACKET_ATTR_HASH
    to the netlink policy.

    Fixes: bd1903b7c459 ("net: openvswitch: add hash info to upcall")
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>
    Reviewed-by: Greg Rose <gvrose8192@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
commit bd1903b7c4596ba6f7677d0dfefd05ba5876707d
Author: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Date:   Wed Nov 13 23:04:49 2019 +0800

    net: openvswitch: add hash info to upcall

    When using the kernel datapath, the upcall don't
    include skb hash info relatived. That will introduce
    some problem, because the hash of skb is important
    in kernel stack. For example, VXLAN module uses
    it to select UDP src port. The tx queue selection
    may also use the hash in stack.

    Hash is computed in different ways. Hash is random
    for a TCP socket, and hash may be computed in hardware,
    or software stack. Recalculation hash is not easy.

    Hash of TCP socket is computed:
    tcp_v4_connect
        -> sk_set_txhash (is random)

    __tcp_transmit_skb
        -> skb_set_hash_from_sk

    There will be one upcall, without information of skb
    hash, to ovs-vswitchd, for the first packet of a TCP
    session. The rest packets will be processed in Open vSwitch
    modules, hash kept. If this tcp session is forward to
    VXLAN module, then the UDP src port of first tcp packet
    is different from rest packets.

    TCP packets may come from the host or dockers, to Open vSwitch.
    To fix it, we store the hash info to upcall, and restore hash
    when packets sent back.

    +---------------+          +-------------------------+
    |   Docker/VMs  |          |     ovs-vswitchd        |
    +----+----------+          +-+--------------------+--+
         |                       ^                    |
         |                       |                    |
         |                       |  upcall            v restore packet hash
(not recalculate)
         |                     +-+--------------------+--+
         |  tap netdev         |                         |   vxlan module
         +--------------->     +-->  Open vSwitch ko     +-->
           or internal type    |                         |
                               +-------------------------+

    Reported-at: https://mail.openvswitch.org/pipermail/ovs-dev/2019-October/364062.html
    Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
    Acked-by: Pravin B Shelar <pshelar@ovn.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Tested-by: Aliasgar Ginwala <aginwala@ebay.com>
Acked-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Signed-off-by: Han Zhou <hzhou@ovn.org>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>