Handle DLT_PFLOG on all OSes.

Handle DLT_PFLOG on all OSes.

Don't pad the pflog header with BPF_WORDALIGN(); round up to a multiple
of 4, instead, as that's what all but FreeBSD do, and FreeBSD used to do
that and should go back to doing so (kern/261566).

Don't rely on the OS's pflog include files to define direction types,
reason types, action types, or the layout of the header; instead, define
them ourselves in a header of our own, with #ifs to select the ones that
are only on some platforms.  That way, it'll handle some fields and
field values (the ones common to all OSes with pflog) on all OSes, even
ones without pflog.

That also expands the set of direction, reason, and action codes to what
various *BSDs and Darwin support.

Also, handle all the different AF_INET6 values in various *BSDs and
Darwin.