datapath:backport: openvswitch: use flow protocol when recalculating ipv6 checksums

datapath:backport: openvswitch: use flow protocol when recalculating ipv6 checksums

Upstream commit:
    commit b4f70527f052b0c00be4d7cac562baa75b212df5
    Author: Simon Horman <simon.horman@netronome.com>
    Date:   Thu Apr 21 11:49:15 2016 +1000

    openvswitch: use flow protocol when recalculating ipv6 checksums

    When using masked actions the ipv6_proto field of an action
    to set IPv6 fields may be zero rather than the prevailing protocol
    which will result in skipping checksum recalculation.

    This patch resolves the problem by relying on the protocol
    in the flow key rather than that in the set field action.

    Fixes: 83d2b9ba1abc ("net: openvswitch: Support masked set actions.")
    Cc: Jarno Rajahalme <jrajahalme@nicira.com>
    Signed-off-by: Simon Horman <simon.horman@netronome.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Pravin B Shelar <pshelar@ovn.org>
Acked-by: Jesse Gross <jesse@kernel.org>