CVE-2026-53211: netfilter: nft_meta_bridge: fix stale stack leak via IIFHWADDR register

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nftmetabridge: fix stale stack leak via IIFHWADDR register

NFTMETABRIIIFHWADDR declares its destination register with len = ETHALEN (6 bytes), which the register-init tracking rounds up to two 32-bit registers (8 bytes). nftmetabridgegeteval() then does memcpy(dest, brdev->devaddr, ETHALEN), writing only 6 bytes and leaving the upper 2 bytes of the second register as uninitialised nftdochain() stack. A downstream load of that register span leaks those stale bytes to userspace.

Zero the second register before the memcpy so the full declared span is written.