CVE-2017-13027/LLDP: Fix a bounds check.

The total length of the OID is the OID length plus the length of the OID
length itself.

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

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