cfg80211: don't skip multi-bssid index element

When creating the IEs for the nontransmitted BSS, the index
element is skipped. However, we need to get DTIM values from
it, so don't skip it.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>