optimize the sync worker
optimize the sync worker

This change optimize the sync worker when we only have to listen on one
interface. While I'm here, I fixed a long and unnoticed outstanding issue when
we were accepting on multiple interfaces (wonder if someone really use it), at
some point soe interfaces were skipped.

elelianghh/gunicorn,mvaled/gunicorn,gtrdotmcs/gunicorn,zhoucen/gunicorn,prezi/gunicorn,z-fork/gunicorn,malept/gunicorn,jamesblunt/gunicorn,prezi/gunicorn,malept/gunicorn,gtrdotmcs/gunicorn,jamesblunt/gunicorn,mvaled/gunicorn,ephes/gunicorn,beni55/gunicorn,malept/gunicorn,mvaled/gunicorn,zhoucen/gunicorn,jamesblunt/gunicorn,tempbottle/gunicorn,zhoucen/gunicorn,MrKiven/gunicorn,1stvamp/gunicorn,prezi/gunicorn,ccl0326/gunicorn,ccl0326/gunicorn,harrisonfeng/gunicorn,1stvamp/gunicorn,WSDC-NITWarangal/gunicorn,tejasmanohar/gunicorn,gtrdotmcs/gunicorn,keakon/gunicorn,1stvamp/gunicorn,GitHublong/gunicorn,ccl0326/gunicorn