netfilter: nft_meta_bridge: fix stale stack leak via IIFHWADDR register

In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_meta_bridge: fix stale stack leak via IIFHWADDR register NFT_META_BRI_IIFHWADDR declares its destination register with len = ETH_ALEN (6 bytes), which the register-init tracking rounds up to two 32-bit registers (8 bytes). nft_meta_bridge_get_eval() then does memcpy(dest, br_dev->dev_addr, ETH_ALEN), writing only 6 bytes and leaving the upper 2 bytes of the second register as uninitialised nft_do_chain() 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.