gossip: Add default constructor for gossip_digest_ack
gossip: Add default constructor for gossip_digest_ack

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