wifi: iwlwifi: mld: tests: extend link pair tests

Generalize and extend the link pair tests to not just do
channel load checks, but generally check link pairs. To
enable more accurate checking, return the reasons bitmap
from iwl_mld_valid_emlsr_pair() and therefore rename it
to iwl_mld_emlsr_pair_state.

It's also necessary now to add more chandefs, and while
doing so fix the existing ones to be valid and add a
test to check they really are valid.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250430151952.1f7c4ac75c6d.I69d68359e02d99632e95daba3d126115dce167b3@changeid