userspace: Support for push_eth and pop_eth actions

userspace: Support for push_eth and pop_eth actions

Add support for actions push_eth and pop_eth to the netdev datapath and
the supporting libraries. This patch relies on the support for these actions
in the kernel datapath to be present.

Signed-off-by: Lorand Jakab <lojakab@cisco.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: Yi Yang <yi.y.yang@intel.com>
Signed-off-by: Jean Tourrilhes <jt@labs.hpe.com>
Signed-off-by: Jan Scheurich <jan.scheurich@ericsson.com>
Co-authored-by: Zoltan Balogh <zoltan.balogh@ericsson.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>