h2o_mem_swap only swaps the first 256 bytes at most
h2o_mem_swap only swaps the first 256 bytes at most

Have the function increment `x` and `y` so that all the blocks are
swapped. This doesn't affect the current code as the only caller uses a
structure smaller than 256 bytes.

Reported by Tim Newsham

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