datapath: more accurate checksumming in queue_userspace_packet()

datapath: more accurate checksumming in queue_userspace_packet()

Upstream commit:
    commit 7529390d08f07fbf9b0174c5a87600b5caa1a8e8
    Author: Davide Caratti <dcaratti@redhat.com>
    Date:   Thu May 18 15:44:42 2017 +0200

    openvswitch: more accurate checksumming in queue_userspace_packet()

    if skb carries an SCTP packet and ip_summed is CHECKSUM_PARTIAL, it needs
    CRC32c in place of Internet Checksum: use skb_csum_hwoffload_help to avoid
    corrupting such packets while queueing them towards userspace.

    Signed-off-by: Davide Caratti <dcaratti@redhat.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Joe Stringer <joe@ovn.org>