reduce the use of stack in BPF programs
reduce the use of stack in BPF programs

See https://github.com/h2o/h2o/pull/3049#discussion_r918482711 for the
discussion.

yannick/h2o,h2o/h2o,devnexen/h2o,devnexen/h2o,devnexen/h2o,h2o/h2o,h2o/h2o,yannick/h2o,yannick/h2o,devnexen/h2o,yannick/h2o,devnexen/h2o,h2o/h2o,h2o/h2o,yannick/h2o,devnexen/h2o,devnexen/h2o,h2o/h2o,yannick/h2o,devnexen/h2o,yannick/h2o,h2o/h2o,yannick/h2o,devnexen/h2o,yannick/h2o,h2o/h2o,h2o/h2o