pcap_datalink_name_to_val(3) on FreeBSD

The text 397621006f31, as FreeBSD 8.4-RELEASE, FreeBSD 8.3-RELEASE, FreeBSD 8.2-RELEASE, FreeBSD 8.1-RELEASE, FreeBSD 8.0-RELEASE shipped it.

get the link-layer header type value corresponding to a header type name