wlan: Use split scan when in STA+SAP concurrency

In STA+SAP concurrency, scan requests received on STA
interface when not in connected state are not split.
This can result in large time gap between successive beacons
sent by SAP.

Fix is to split scan in case of STA+SAP concurrency when
STA is not connected as well.

Change-Id: I9ba0928b154ff64ee478d4d1ac215876a039bd1e
CRs-Fixed: 2314202