Rewrite get_ip() method to use PHP native functions in uploads-by-proxy

The present implementation of get_ip() relies on querying remote websites, one of which, hostnametoip.com, is no longer around, leading to an error cascade which breaks the plugin's functioning.

The line referencing this domain can be safely commented out, but it's more portable and reliable to use PHP's built-in functions for DNS lookups. The end result is this patch which has a rewrite for the get_ip method.