net: sockets: getaddrinfo() buffer overflow, etc. fixes

The existing implementation assumed DNS resolv callback will be
called just once, but that's not always the case (apparently,
for multi-homes hosts or something). So, apply array bounds
checking (and do pointer arithmetic only after it, as the C
standard otherwise warns of "undefined behavior"). In such a case,
the port number wasn't set in each entry too, so rework how it's
done.

The issues discovered while resolving archive.ubuntu.com.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>