option.c: use rb_w32_inet_pton

* ext/socket/option.c (inet_pton): use rb_w32_inet_pton, instead of
  inet_ntop directly, which is unavailable on older version Windows.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45151 b2dd03c8-39d4-4d8f-98ff-823fe69b080e