Unbreak pfe_ctrl by building with WIFI_ENABLE=y

Previously, we were not able to transmit Ethernet frames using pfe_ctrl.
Mindspeed advised in Mindzilla bug 77600 to set WIFI_ENABLE=y which
fixes the problem.
diff --git a/Makefile b/Makefile
index de88258..8a10fbe 100644
--- a/Makefile
+++ b/Makefile
@@ -12,7 +12,7 @@
 		$(DESTDIR)/sbin/hotplug
 
 pfe_ctrl/all:
-	$(MAKE) -C pfe_ctrl $(LINUX_MAKE_FLAGS) KERNELDIR=$(LINUX_DIR) PFE_DIR=../pfe
+	$(MAKE) -C pfe_ctrl $(LINUX_MAKE_FLAGS) KERNELDIR=$(LINUX_DIR) PFE_DIR=../pfe WIFI_ENABLE=y
 
 pfe_ctrl/install:
 	$(MAKE) -C $(LINUX_DIR) $(LINUX_MAKE_FLAGS) M="$(shell /bin/pwd)/pfe_ctrl" modules_install