Revert "There is no need to set KERNEL_DIR anymore now linux-mod-r1 is fixed"

This reverts commit 81dcbb3.

Author: sayanchowdhury

sdk_container/src/third_party/coreos-overlay/coreos/config/env/sys-fs/zfs-kmod

@@ -1,3 +1,6 @@
+: ${MODULES_ROOT:=$(echo ${SYSROOT}/lib/modules/*)}
+KERNEL_DIR="${MODULES_ROOT}/build"
+
 # This addresses an issue with the kernel version compatibility check
 #  when installing zfs-kmod to /build/<arch> (e.g. via build_packages)
 #  from its binpkg (i.e. not recompiling it).