BPF extensions

[Joerg Sonnenberger]

Hi all,
a patch waits at http://leaf.dragonflybsd.org/~joerg/bpf.diff
to be tested e.g. with wi(4) devices. It adds the long pushed
back support for multiple data link types on one interface
and does some general cleanup of the BPF usage.

If you want to the the multiple data link types with wi(4),
keep in mind to rebuild libpcap with current header files or
do a buildworld.

TTC: Wednesday

Joerg