Fix getting value of CONFIG_BCM_WIFI_MFGTEST when set in iopsyswrt/.config
Setting CONFIG_BCM_WIFI_MFGTEST to y in .config file in iopsyswrt wasn't being detected by bcmkernel makefile, so the change in this MR will make it work.
Setting CONFIG_BCM_WIFI_MFGTEST to y in .config file in iopsyswrt wasn't being detected by bcmkernel makefile, so the change in this MR will make it work.