wifi: iwlwifi: mld: refactor tests to use chandefs

Instead of building invalid chandefs on the fly, use only
chandefs throughout and ensure those are valid. Also add
more chandefs that will be needed for new tests.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250430151952.6643fa8773f1.I644e9053d222a772e1d109799c4bfa0677add4d7@changeid