Fix compile warning in unit test
Fix compile warning in unit test

```
t/00unit/test.c:74:31: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
     conn->_ostr_final.do_send = loopback_on_send;j
```

deweerdt/h2o,rayrapetyan/h2o,i110/h2o,yannick/h2o,lkwg82/h2o,i110/h2o,yannick/h2o,yannick/h2o,lkwg82/h2o,zlm2012/h2o,cwyang/h2o,rayrapetyan/h2o,deweerdt/h2o,lkwg82/h2o,devnexen/h2o,cwyang/h2o,yannick/h2o,devnexen/h2o,rayrapetyan/h2o,i110/h2o,cubicdaiya/h2o,h2o/h2o,cubicdaiya/h2o,cwyang/h2o,i110/h2o,cubicdaiya/h2o,tamediadigital/h2o,cubicdaiya/h2o,h2o/h2o,i110/h2o,zlm2012/h2o,h2o/h2o,tamediadigital/h2o,yannick/h2o,yannick/h2o,tamediadigital/h2o,zlm2012/h2o,i110/h2o,i110/h2o,rayrapetyan/h2o,lkwg82/h2o,i110/h2o,devnexen/h2o,tamediadigital/h2o,lkwg82/h2o,cubicdaiya/h2o,zlm2012/h2o,cwyang/h2o,lkwg82/h2o,deweerdt/h2o,rayrapetyan/h2o,deweerdt/h2o,cwyang/h2o,lkwg82/h2o,cubicdaiya/h2o,h2o/h2o,devnexen/h2o,lkwg82/h2o,zlm2012/h2o,zlm2012/h2o,yannick/h2o,deweerdt/h2o,rayrapetyan/h2o,rayrapetyan/h2o,zlm2012/h2o,h2o/h2o,deweerdt/h2o,cwyang/h2o,i110/h2o,h2o/h2o,devnexen/h2o,rayrapetyan/h2o,zlm2012/h2o,rayrapetyan/h2o,deweerdt/h2o,devnexen/h2o,tamediadigital/h2o,deweerdt/h2o,cwyang/h2o,tamediadigital/h2o,devnexen/h2o,h2o/h2o,yannick/h2o,i110/h2o,cwyang/h2o,lkwg82/h2o,h2o/h2o,tamediadigital/h2o,yannick/h2o,cubicdaiya/h2o,devnexen/h2o,rayrapetyan/h2o,tamediadigital/h2o,cubicdaiya/h2o,zlm2012/h2o,h2o/h2o,deweerdt/h2o,tamediadigital/h2o,devnexen/h2o