Previously, IBSS mode (NL80211_IFTYPE_ADHOC) was left in drv->nlmode
when leaving IBSS. This causes issues for send_mlme() handler for P2P
Probe Response transmission in Listen state. Fix this by clearing nlmode
back to NL80211_IFTYPE_STATION on leaving IBSS so that following P2P
operations can be executed correctly. Previously, this was fixed only
when the next authentication/association attempt in station mode
occured.