[2.7] bpo-33542: Ignore DUID in uuid.get_node on Windows. (GH-6922) (GH-7015)

[2.7] bpo-33542: Ignore DUID in uuid.get_node on Windows. (GH-6922) (GH-7015)

uuid._ipconfig_getnode did not validate the maximum length of the value,
so long as the value had the same type of formatting as a MAC address.
This let it select DUIDs as MAC addresses. It now requires an exact
length match..
(cherry picked from commit c66c342cb42ab8a88884527ddfe3a5086bc06316)

Co-authored-by: CtrlZvi <viz+github@flippedperspective.com>