h2olog: remove redundant (n|v)_len variables
h2olog: remove redundant (n|v)_len variables

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