wifi: mac80211: mlme: don't add empty EML capabilities

Draft P802.11be_D2.1, section 35.3.17 states that the EML Capabilities
Field shouldn't be included in case the device doesn't have support for
EMLSR or EMLMR.

Fixes: 81151ce4 ("wifi: mac80211: support MLO authentication/association with one link")
Signed-off-by: Mordechay Goodstein <mordechay.goodstein@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>