[mruby/middleware.c] Fix invalid read on the stack
[mruby/middleware.c] Fix invalid read on the stack

`*((struct sockaddr_storage *)&sin);` would cause a read that's larger
than `sin`, reaching to other parts of the stack. We fix this with a
memcpy that only reads `sizeof(sin);` bytes.

devnexen/h2o,yannick/h2o,h2o/h2o,cwyang/h2o,devnexen/h2o,cwyang/h2o,h2o/h2o,deweerdt/h2o,cwyang/h2o,yannick/h2o,yannick/h2o,h2o/h2o,deweerdt/h2o,devnexen/h2o,devnexen/h2o,devnexen/h2o,yannick/h2o,cwyang/h2o,h2o/h2o,h2o/h2o,yannick/h2o,cwyang/h2o,cwyang/h2o,h2o/h2o,devnexen/h2o,deweerdt/h2o,yannick/h2o,deweerdt/h2o,cwyang/h2o,yannick/h2o,deweerdt/h2o,deweerdt/h2o,deweerdt/h2o,h2o/h2o,cwyang/h2o,deweerdt/h2o,h2o/h2o,devnexen/h2o,devnexen/h2o,yannick/h2o,devnexen/h2o,yannick/h2o,deweerdt/h2o,h2o/h2o