/usr/lib/libpacketdump/link_17.protocol is in libpacketdump3v5 3.0.21-1ubuntu2.
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"
 |