{getaddrinfo,getnameinfo}.c: fix for old platforms

* ext/socket/{getaddrinfo,getnameinfo}.c: define socklen_t if not
  defined, e.g., older VC.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40568 b2dd03c8-39d4-4d8f-98ff-823fe69b080e