do nothing in `adjust_conn_linkedlist` if conn is already unlinked (happens when enqueue_goaway is called in advance)
do nothing in `adjust_conn_linkedlist` if conn is already unlinked (happens when enqueue_goaway is called in advance)

yannick/h2o,devnexen/h2o,lkwg82/h2o,cwyang/h2o,devnexen/h2o,devnexen/h2o,devnexen/h2o,deweerdt/h2o,deweerdt/h2o,devnexen/h2o,lkwg82/h2o,yannick/h2o,h2o/h2o,yannick/h2o,yannick/h2o,yannick/h2o,deweerdt/h2o,devnexen/h2o,h2o/h2o,lkwg82/h2o,yannick/h2o,yannick/h2o,cwyang/h2o,h2o/h2o,cwyang/h2o,lkwg82/h2o,yannick/h2o,cwyang/h2o,devnexen/h2o,deweerdt/h2o,devnexen/h2o,deweerdt/h2o,lkwg82/h2o,cwyang/h2o,lkwg82/h2o,h2o/h2o,lkwg82/h2o,deweerdt/h2o,cwyang/h2o,cwyang/h2o,lkwg82/h2o,cwyang/h2o,h2o/h2o,h2o/h2o,devnexen/h2o,deweerdt/h2o,deweerdt/h2o,lkwg82/h2o,h2o/h2o,yannick/h2o,deweerdt/h2o,h2o/h2o,h2o/h2o