* Better parsing/error-checking of VXLAN and encapsulated packet headers
* Add/implement the "vxlan_packet" event
* Add "Tunnel::vxlan_ports" option to tune the set of VXLAN ports to
analyze/decapsulate
* Add "Tunnel::validate_vxlan_checksums" option to allow for tuning of how
checksums associated with the outer UDP header of a possible VXLAN
tunnel are handled
Fixes GH-250
