wifi: iwlwifi: mld: add a debug level for EHT prints

This is required for EHT related debug prints.
As there are no more available debug levels, delete IWL_DL_EXTERNAL,
which is not used, and replace it with IWL_DL_EHT.

Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250212073923.9b1e0d87e7e4.Iea6c1329f7b6312a73896f9a9d9bce72bd6548e2@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>