tools: ynl: ethtool: fix pylint issues

tools: ynl: ethtool: fix pylint issues

Fix or suppress all the pylint issues in ethtool.py, except for
TODO (fixme) items.

Suppress:

- too-many-locals
- too-many-branches
- too-many-statements
- too-many-return-statements
- import-error

Fix:

- missing-module-docstring
- redefined-outer-name
- dangerous-default-value
- use-dict-literal
- missing-function-docstring
- global-variable-undefined
- expression-not-assigned
- inconsistent-return-statements
- wrong-import-order

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20260108161339.29166-9-donald.hunter@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>