pass sizeof(struct sockaddr_in) for AF_INET instead of always using
sizeof(struct sockaddr_in6). also skip getnameinfo entirely for
non-matching interfaces rather than calling it for every entry.

replace strcpy of interface name into ifr_name (IFNAMSIZ=16) with
bounds-checked snprintf. add one byte to resp buffer so NUL-terminating
the SSID at resp boundary does not write out of bounds.