Kernel-stack disclosure via uncleared skbmod padding

Use of uninitialized data in affected Linux kernels allows local users to read four kernel-stack bytes through a netlink reply. tcf_skbmod_dump() serializes struct tc_skbmod without first clearing its four-byte padding hole, returning uninitialized stack contents to user space. The disclosure requires local low-privileged access to the traffic-control netlink path and is bounded to four bytes in each affected dump.