ICMP6 RPL: Add a test capture file

ICMP6 RPL: Add a test capture file

This capture file triggered a buffer over-read with the 4.9.2 release
fixed in the 4.9.3 release.

With the new GET_ macros, the problem no longer exists.
Thus no fix needed.

The pcap file was updated to avoid pcap_loop() error messages.
It was rename from pcapng to pcap because it is.

Update the output of the test accordingly.

Partial update from d7505276842e85bfd067fa21cdb32b8a2dc3c5e4
in 4.9 branch.