Avoid using a class variable in socket specs

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58748 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/rubyspec/library/socket/fixtures/classes.rb

@@ -35,7 +35,7 @@ module SocketSpecs
   end
 
   def self.port
-    @@_port ||= find_available_port
+    @port ||= find_available_port
   end
 
   def self.str_port