iwlwifi: mvm: add debugfs entry to configure netdetect SSIDs

Before we get all the chain (ie. mac80211, cfg80211, nl80211 and
userspace) changed to support net-detect, we can use this debugfs
entry for easy testing and as a proof of concept.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>