replace invalid wireshark manufacturer database link in unique generator

[ghostserverd]

relates to https://github.com/sickcodes/Docker-OSX/issues/681

The manufacturer list currently referenced by the machine value generator script no longer exists resulting in a 404 and no unique device identifiers generated.

That manufacturer list is now populating automatically at the address in this change (see this issue for more details).

Tested by running

./custom/generate-unique-machine-values.sh

from this branch.