This seems to be a copy-paste error. The `GNRCICMPv6EchoParser` parse
function parses of course the output of the `ping6` command, not the
`nib neigh show` command.
Found during integration of release tests:
- if the payload is too small, RTTs are not shown
- duplicates are now shown properly, if duplicates exist, the stats are
now parsed instead of ignored