ofp-util: Add OpenFlow 1.5 packet-out support

ofp-util: Add OpenFlow 1.5 packet-out support

This patch implements the encoding and decoding of the new packet-out
format defined in OpenFlow 1.5. Test cases are provided to verify the
encoding and decoding.

This patch is based on [1] and [2].

[1] https://github.com/jean2/openvswitch/commits/jean/ext-427
[2] https://mail.openvswitch.org/pipermail/ovs-dev/2017-April/331032.html

Signed-off-by: Jean Tourrilhes <jt@labs.hpe.com>
Signed-off-by: Zoltan Balogh <zoltan.balogh@ericsson.com>
Co-authored-by: Jan Scheurich <jan.scheurich@ericsson.com>
Signed-off-by: Yi-Hung Wei <yihung.wei@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>