unaligned pointer: nd_opt_prefix_info.nd_opt_pi_prefix

[robbat2]

https://github.com/radvd-project/radvd/actions/runs/12590121353/job/35091122758?pr=253#step:3:1771

  process.c:289:38: warning: taking address of packed member 'nd_opt_pi_prefix' of class or structure 'nd_opt_prefix_info' may result in an unaligned pointer value [-Waddress-of-packed-member]
    289 |                                     addr_match(&prefix->Prefix, &pinfo->nd_opt_pi_prefix, prefix->PrefixLen)) {
        |                                                                  ^~~~~~~~~~~~~~~~~~~~~~~

--- radvdump.o ---
  radvdump.c:330:15: warning: taking address of packed member 'nd_opt_pi_prefix' of class or structure 'nd_opt_prefix_info' may result in an unaligned pointer value [-Waddress-of-packed-member]
    330 |                         addrtostr(&pinfo->nd_opt_pi_prefix, prefix_str, sizeof(prefix_str));
        |                                    ^~~~~~~~~~~~~~~~~~~~~~~