qcacld-3.0: Send DISCONNECT event to IPA in roaming

Send STA_DISCONNECT event to IPA before sending STA_CONNECT in roaming
scenario. This is needed by IPA to cleanup in roaming scenario. Without
the event, IPA may not be able to setup routing tables in IPA hardware
properly.

Change-Id: I694736654a137718cd250c28d3c4681a1007ce9a
CRs-Fixed: 2739550