CVE-2017-13016/ES-IS: Fix printing of addresses in RD PDUs.

Always print the SNPA, and flag it as such; only print it as a MAC
address if it's 6 bytes long.

Identify the NET as such.

This fixes a buffer over-read discovered by Bhargava Shastry,
SecT/TU Berlin.

Add tests using the capture files supplied by the reporter(s), modified
so the capture files won't be rejected as an invalid capture.