disable reverse lookup by default. [ruby-core:45514] [Feature #6559]
Socket.do_not_reverse_lookup is true by default but WEBrick
overwrote it.
patch by Eric Hodel [ruby-core:45527]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55881 b2dd03c8-39d4-4d8f-98ff-823fe69b080e