datapath: enable NSH support

datapath: enable NSH support

Upstream commit:
  commit b2d0f5d5dc53532e6f07bc546a476a55ebdfe0f3
  Author: Yi Yang <yi.y.yang@intel.com>
  Date:   Tue Nov 7 21:07:02 2017 +0800

    openvswitch: enable NSH support

    OVS master and 2.8 branch has merged NSH userspace
    patch series, this patch is to enable NSH support
    in kernel data path in order that OVS can support
    NSH in compat mode by porting this.

    Signed-off-by: Yi Yang <yi.y.yang@intel.com>
    Acked-by: Jiri Benc <jbenc@redhat.com>
    Acked-by: Eric Garver <e@erig.me>
    Acked-by: Pravin Shelar <pshelar@ovn.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Yi Yang <yi.y.yang@intel.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Reviewed-by: Greg Rose <gvrose8192@gmail.com>