mruby-socket/socket.c: include Socket::Constants in C init

mrbgems/mruby-socket/mrblib/socket.rb

@@ -570,8 +570,4 @@ class UNIXServer < UNIXSocket
   end
 end
 
-class Socket
-  include Constants
-end
-
 class SocketError < StandardError; end

mrbgems/mruby-socket/src/socket.c

@@ -1082,6 +1082,8 @@ mrb_mruby_socket_gem_init(mrb_state* mrb)
   } while (0)
 
 #include "const.cstub"
+
+  mrb_include_module(mrb, sock, constants);
 }
 
 void