wlan: Trigger sta cleanup only in link_est state

In SAP mode, auth frame is received immediately after
assoc frame but before add sta response is received.
This will result in disconnection and cleanup. As part
of disassoc indication to csr, hdd_hostapd_SAPEventCB
will get triggered with eSAP_STA_LOSTLINK_DETECTED event
and since add sta is not done, invalid sta index is
populated in disassoc_event.

Fix is to drop the auth frame until mlm state moves to
link_established.

Change-Id: If90745c04de79a337f50b5450fea0de810ba5a69
CRs-Fixed: 2513500