Busybox: Enable IPv6 ping & traceroute

...for some reason, these are not enabled by its config even though IPv6
is on by default.

Change-Id: Ie9763c35ca07326b400638eda65d737e72eb63fb
diff --git a/configs/czechlight_beaglebone_defconfig b/configs/czechlight_beaglebone_defconfig
index db32ccb..37d2abe 100644
--- a/configs/czechlight_beaglebone_defconfig
+++ b/configs/czechlight_beaglebone_defconfig
@@ -21,6 +21,7 @@
 BR2_LINUX_KERNEL_DTS_SUPPORT=y
 BR2_LINUX_KERNEL_USE_CUSTOM_DTS=y
 BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/beaglebone/czechlight-bbb.dts"
+BR2_PACKAGE_BUSYBOX_CONFIG_FRAGMENT_FILES="$(BR2_EXTERNAL_CZECHLIGHT_PATH)/board/czechlight/common/busybox-config"
 BR2_PACKAGE_AVAHI=y
 BR2_PACKAGE_AVAHI_DAEMON=y
 BR2_PACKAGE_OPENSSH=y