DLT and LINKTYPE allocation
  ===========================
  
  DLT_ types live in pcap/dlt.h.  They can be requested by the community on a
  First-Come First-Served basis [i.e. https://tools.ietf.org/html/rfc8126#section-4.4 ]
  (Although libpcap is not at this time an IETF specification, there have been
  some as yet-incomplete efforts to do this).
  
  The Tcpdump Group prefers to link to an open specification on the new DLT_
  type,  but they are available for closed, proprietary projects as well.
  In that case, a stable email address suffices so that someone who finds
  an unknown DLT_ type can investigate.
  We prefer to give out unambiguous numbers, and we try to do it as quickly
  as possible, but DLT_USERx is available while you wait.
  
  Note that DLT_ types are, in theory, private to the capture mechanism and can
  in some cases be operating system specific, and so a second set of values,
  LINKTYPE_ is allocated for actually writing to pcap files.  As much as
  possible going forward, the DLT_ and LINKTYPE_ value are identical, however,
  this was not always the case.  See pcap-common.c.
  
  The LINKTYPE_ values are not exported, but are in pcap-common.c only.
  
  DEVELOPER NOTES
  ---------------
  
  When allocating a new DLT_ value, a corresponding value needs to be
  added to pcap-common.c.
  It is not necessary to copy the comments from dlt.h to pcap-common.c.