ibrowse_socks5: fix 'can't find include lib "kernel/src/inet_dns.hrl"'

This commit should fix the 'can't find include lib "kernel/src/inet_dns.hrl"' issue, because we will not use internal header files. Also this commit removes some hardcode ( -define(DNS_IP, {8,8,8,8}) ) and uses a convenient way to get a host IP address.

P.S. I didn't test it because I haven't a socks5 proxy.