mac80211: ibss - do not scan if not needed when creating an IBSS

In some cases mac80211 will scan before creating an IBSS
even if bssid and frequency have been forced by the user.
This is not needed and leads only to a delay in the IBSS
establishment phase.

Immediately create the cell if both bssid and frequency
(and fixed_freq is set) have been specified.

Signed-off-by: Antonio Quartulli <antonio@open-mesh.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>