[th/ethtool-eee-enabled] libnm: rename "ethtool.eee" property to "ethtool.eee-enabled"

There are various properties related to EEE, that we might want to add support for in the future (for example, "ethtool.eee-advertise").

Don't use up the base name "eee", instead make it "eee-enabled". All properties should have different prefixes, and "ethtool.eee" would be a prefix of "ethtool.eee-advertise".

Rename.

Fixes: 3165d9a2 ('ethtool: introduce EEE support')

CC: @dickenhobelix