sstable: use desired buffer size in write_simple
sstable: use desired buffer size in write_simple

Currently, we use a 128k buffer for creation of data and index
files, but for other components we use a 4k buffer size.
Let's also use a 128k buffer for the other components.

Signed-off-by: Raphael S. Carvalho <1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@cloudius-systems.com>

glommer/scylla,acbellini/scylla,victorbriz/scylla,rentongzhang/scylla,shaunstanislaus/scylla,gwicke/scylla,linearregression/scylla,victorbriz/scylla,capturePointer/scylla,guiquanz/scylla,tempbottle/scylla,scylladb/scylla,rluta/scylla,eklitzke/scylla,kjniemi/scylla,rentongzhang/scylla,eklitzke/scylla,aruanruan/scylla,kangkot/scylla,acbellini/scylla,respu/scylla,phonkee/scylla,shaunstanislaus/scylla,wildinto/scylla,bowlofstew/scylla,kangkot/scylla,stamhe/scylla,dwdm/scylla,justintung/scylla,glommer/scylla,raphaelsc/scylla,gwicke/scylla,phonkee/scylla,scylladb/scylla,dwdm/scylla,acbellini/scylla,duarten/scylla,avikivity/scylla,respu/scylla,scylladb/scylla,phonkee/scylla,linearregression/scylla,raphaelsc/scylla,justintung/scylla,senseb/scylla,senseb/scylla,wildinto/scylla,rluta/scylla,kangkot/scylla,duarten/scylla,rentongzhang/scylla,linearregression/scylla,dwdm/scylla,guiquanz/scylla,asias/scylla,capturePointer/scylla,aruanruan/scylla,stamhe/scylla,aruanruan/scylla,scylladb/scylla,capturePointer/scylla,bowlofstew/scylla,shaunstanislaus/scylla,gwicke/scylla,rluta/scylla,stamhe/scylla,asias/scylla,wildinto/scylla,bowlofstew/scylla,guiquanz/scylla,duarten/scylla,raphaelsc/scylla,respu/scylla,victorbriz/scylla,eklitzke/scylla,asias/scylla,tempbottle/scylla,avikivity/scylla,avikivity/scylla,justintung/scylla,kjniemi/scylla,glommer/scylla,tempbottle/scylla,kjniemi/scylla,senseb/scylla