NetBSD support for multiple data link types on an interface, from David

NetBSD support for multiple data link types on an interface, from David
Young <[email protected]>, with some minor changes by Jason R.  Thorpe
<[email protected]>, and further changes by me to support it on BPF
systems lacking BIOCGDLTLIST and other platforms lacking an equivalent
feature.

Update Jason Thorpe's e-mail address (Zembu is going away, if it hasn't
done so already).

Add APIs to map DLT names to DLT values and vice versa.