/usr/lib/libpacketdump/link_17.protocol is in libpacketdump3 3.0.18-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 | # PPP (RFC1661)
be8	hex	"PPP: Address"
be8	hex	"PPP: Control"
le16	hex	"PPP: Type"
next	"ppp"	"PPP: Type"
 |