qcacld-3.0: enable DP pending memory flushing

Enable DP pending memory flushing by macro WLAN_DP_PENDING_MEM_FLUSH.

DP references of the peer will be removed once we receive PEER
unmap message from the firmware. If the firmware has failed to
send the peer unmap message (due to an assert in FW), then the
peer entries will remain the inactive peer list and will trigger
a explicit QDF_BUG() during driver unload.
Force clean the inactive peer/vdev list during driver unload in such
cases.

Change-Id: I2565cd4f1a4afea8536bcca86147d6fa028be554
CRs-Fixed: 2988733

configs/qca6390_defconfig

@@ -826,3 +826,5 @@ CONFIG_WLAN_BOOTUP_MARKER := y
 endif
 
 CONFIG_WLAN_SYSFS_MEM_STATS := y
+
+CONFIG_WLAN_DP_PENDING_MEM_FLUSH := y