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.