wlan: Remove the NULL SSID check from AP caps mismatch logic.

In limDetectChangeInApCapabilities if SSID is NULL DUT sends an
unicast probe request to AP and recheck the capability once
it gets the probe resp.Some APs sends NULL SSID even in Probe
resp and thus AP is disconnected.

Removed the NULL SSID check from limDetectChangeInApCapabilities.

Change-Id: Ie195b8ab9a0e24e5c6082d62090cfa7c22ee3ccc
CRs-Fixed: 669282