wlan: Fix missing sta_id hash attach in ap mode

Sta_id attach to mac address hash is expected to be done after AP mode
initialization. But it is missing in few scenarios. This is resulting
in STA connection failure to SAP.

To resolve this, attach sta_id to mac address hash as part of ap mode
initialization.

Change-Id: If039b201af9806873aa6751caf7bb455275760d6
CRs-Fixed: 2825333