Use current addrinfo entry in #XGETADDRINFO result iteration

[Copilot]

The reviewed issue pointed out that AT#XGETADDRINFO iterated addrinfo results but read result->ai_addr (head node) instead of the current loop node, which can return incorrect addresses when multiple DNS results are present.
This update scopes to that comment and aligns address selection with the active iterator entry.

• AT#XGETADDRINFO address selection

  • In handle_at_getaddrinfo(), switched IPv4/IPv6 address casts from result->ai_addr to res->ai_addr inside the result loop.
  • This ensures each emitted address comes from the corresponding addrinfo node.

• Regression coverage for multi-result iteration

  • Added a focused unit test for AT#XGETADDRINFO with multiple mocked IPv4 results.
  • Verifies output includes both addresses in order, confirming per-node address handling.

for (res = result; res != NULL; res = res->ai_next) {
    if (res->ai_family == NRF_AF_INET) {
        struct nrf_sockaddr_in *host =
            (struct nrf_sockaddr_in *)res->ai_addr;
    } else if (res->ai_family == NRF_AF_INET6) {
        struct nrf_sockaddr_in6 *host =
            (struct nrf_sockaddr_in6 *)res->ai_addr;
    }
}