netfilter: nft_nat: fully initialise new_addr in netmap setup

In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_nat: fully initialise new_addr in netmap setup nft_nat_setup_netmap() builds the mapped address in an on-stack union nf_inet_addr. For an IPv4 mapping it writes only the 4-byte .ip member and the loop runs a single 32-bit iteration, but it then copies the whole 16-byte union into range->min_addr and range->max_addr, so the upper 12 bytes reach nf_nat_setup_info() uninitialised. KMSAN reports an uninit-value in nf_nat_setup_info() reached from nft_nat_eval(). The IPv6 path fills all 16 bytes and is not affected. Zero-initialise new_addr.