qcacld-3.0: Enable flag to increase TX descs in AUTO QCA6390

Based on multi-clients test experiment, when AUTO SA8155+HST
works as SAP connected more than 8 Ref STA clients, it requires
increase in TX descriptors to burst traffic to each Rx device,
or flow control happens to stop host tx queue frequently for
missing TX descriptors, can't get high throughput.

Change-Id: Ie2adbdd3bfece323d51d5e96fef6001c4e39c3f4
CRs-Fixed: 2703765

configs/qca6390_defconfig

@@ -12,6 +12,7 @@ ifeq ($(CONFIG_CNSS_QCA6390), y)
 	CONFIG_WLAN_FEATURE_DFS_OFFLOAD := y
 	CONFIG_IPA3 := n
 	CONFIG_SCALE_INCLUDES := y
+	CONFIG_MORE_TX_DESC := y
 endif
 
 ifeq ($(CONFIG_ENABLE_IPA), y)