Add to .repo/local_manifests/gtaxlwifi.xml:
<?xml version="1.0" encoding="UTF-8"?>
<manifest>
<project path="device/samsung/gtaxlwifi" name="android_device_samsung_gtaxlwifi" remote="TeamWin" revision="android-6.0" />
</manifest>Then run repo sync to check it out.
Kernel sources are available at: https://github.com/jcadduono/android_kernel_samsung_exynos7870/tree/twrp-6.0