xen: fix explicitly-disabled split event channel feature
xen: fix explicitly-disabled split event channel feature

In case the hypervisor supports the split event channel feature, but
advertises it as disabled, we must not assume it works.

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