pcap_datalink_name_to_val(3) on FreeBSD

The text 053153919eb6, as FreeBSD 12.1-RELEASE, FreeBSD 12.0-RELEASE, FreeBSD 11.3-RELEASE, FreeBSD 11.2-RELEASE, FreeBSD 11.1-RELEASE shipped it.

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