Use inet_pton() in LookupIntern() first

In LookupIntern(), the getaddrinfo_a() call would be issued if it's avaiable, which in turn would kick off a new thread for async name resolving job.  In our code, most calls go to LookupIntern() are just trying to convert a text ip address into a struct but not a real name resolving request, so we should do that first to avoid extra thread overhead.

Signed-off-by: Huang Le <4tarhl@gmail.com>