xen: positively acknowledge supported features
xen: positively acknowledge supported features

Instead of just nacking unsupported features, respond to all features,
with a NACK for unsupported ones and ACK for supported ones.

victorbriz/scylla,capturePointer/scylla,acbellini/seastar,linearregression/scylla,acbellini/seastar,avikivity/scylla,bowlofstew/seastar,leejir/seastar,cloudius-systems/seastar,sjperkins/seastar,stamhe/scylla,asias/scylla,anzihenry/seastar,flashbuckets/seastar,gwicke/scylla,chunshengster/seastar,scylladb/scylla,duarten/scylla,shyamalschandra/seastar,joerg84/seastar,linearregression/seastar,kjniemi/seastar,senseb/scylla,bowlofstew/scylla,scylladb/scylla,dreamsxin/seastar,bzero/seastar,flashbuckets/seastar,kjniemi/seastar,capturePointer/scylla,tempbottle/scylla,tempbottle/seastar,aruanruan/scylla,glommer/scylla,dwdm/scylla,acbellini/scylla,raphaelsc/scylla,syuu1228/seastar,dwdm/scylla,stamhe/scylla,rluta/scylla,bowlofstew/seastar,respu/scylla,raphaelsc/scylla,wildinto/seastar,linearregression/scylla,stamhe/seastar,shaunstanislaus/scylla,scylladb/seastar,joerg84/seastar,wildinto/scylla,kjniemi/seastar,norcimo5/seastar,eklitzke/scylla,gwicke/scylla,scylladb/seastar,glommer/scylla,bzero/seastar,stamhe/seastar,shyamalschandra/seastar,raphaelsc/scylla,linearregression/scylla,tempbottle/scylla,senseb/scylla,hongliangzhao/seastar,linearregression/seastar,joerg84/seastar,duarten/scylla,dreamsxin/seastar,rentongzhang/scylla,chunshengster/seastar,asias/scylla,scylladb/scylla,respu/scylla,jonathanleang/seastar,rluta/scylla,raphaelsc/seastar,kangkot/scylla,kangkot/scylla,hongliangzhao/seastar,kjniemi/scylla,duarten/scylla,bowlofstew/seastar,koolhazz/seastar,anzihenry/seastar,avikivity/seastar,cloudius-systems/seastar,justintung/scylla,dreamsxin/seastar,victorbriz/scylla,xtao/seastar,koolhazz/seastar,dwdm/seastar,rentongzhang/scylla,avikivity/seastar,wildinto/scylla,raphaelsc/seastar,printedheart/seastar,mixja/seastar,leejir/seastar,sjperkins/seastar,shaunstanislaus/scylla,anzihenry/seastar,raphaelsc/seastar,tempbottle/seastar,phonkee/scylla,ducthangho/imdb,victorbriz/scylla,bowlofstew/scylla,eklitzke/scylla,slivne/seastar,hongliangzhao/seastar,avikivity/scylla,bzero/seastar,scylladb/seastar,ducthangho/imdb,mixja/seastar,scylladb/scylla,wildinto/scylla,dwdm/seastar,phonkee/scylla,shaunstanislaus/scylla,scylladb/scylla-seastar,dwdm/scylla,kangkot/scylla,wildinto/seastar,acbellini/seastar,stamhe/scylla,avikivity/scylla,guiquanz/scylla,gwicke/scylla,rluta/scylla,printedheart/seastar,eklitzke/scylla,tempbottle/seastar,sjperkins/seastar,koolhazz/seastar,syuu1228/seastar,scylladb/scylla-seastar,shyamalschandra/seastar,acbellini/scylla,stamhe/seastar,bowlofstew/scylla,slivne/seastar,leejir/seastar,kjniemi/scylla,flashbuckets/seastar,norcimo5/seastar,respu/scylla,glommer/scylla,avikivity/seastar,mixja/seastar,linearregression/seastar,wildinto/seastar,cloudius-systems/seastar,slivne/seastar,printedheart/seastar,rentongzhang/scylla,guiquanz/scylla,norcimo5/seastar,jonathanleang/seastar,syuu1228/seastar,tempbottle/scylla,capturePointer/scylla,ducthangho/imdb,acbellini/scylla,guiquanz/scylla,aruanruan/scylla,scylladb/scylla-seastar,jonathanleang/seastar,phonkee/scylla,aruanruan/scylla,xtao/seastar,kjniemi/scylla,chunshengster/seastar,xtao/seastar,senseb/scylla,justintung/scylla,dwdm/seastar,asias/scylla,justintung/scylla