qcacld-3.0: Enable enahnced flow control

a) Enabled flow control
b) Add small helper functions to avoid duplication of
   code.
c) Fix thermal mitigation unpause issue with flow control.

CRs-Fixed: 916716
Change-Id: Ic02b66d1c23768a1c71dc08ed50dcedd02b647ce

Kbuild

@@ -116,7 +116,11 @@ ifeq ($(KERNEL_BUILD), 0)
 	CONFIG_WLAN_NAPI_DEBUG := n
 
 	# Flag to enable FW based TX Flow control
-	CONFIG_WLAN_TX_FLOW_CONTROL_V2 := n
+	ifeq ($(CONFIG_CNSS_EOS),y)
+		CONFIG_WLAN_TX_FLOW_CONTROL_V2 := y
+	else
+		CONFIG_WLAN_TX_FLOW_CONTROL_V2 := n
+	endif
 
 	# Flag to enable LRO (Large Receive Offload)
 	ifeq ($(CONFIG_CNSS_EOS), y)