wifi: mac80211: separate out connection downgrade flags

wifi: mac80211: separate out connection downgrade flags

Separate out the connection downgrade flags from the ifmgd->flags
and put them into the link information instead. While at it, make
them a separate sparse type so we don't get confused about where
they belong and have static checking on correct handling.

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