This should increase process responsiveness when a single _poll call
fetched many packets: as long as packet queue is not empty, no epoll.poll
call was made. This means that outgoing packets were kept in our buffer
until packet queue becomes empty.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2420 71dcc9de-d417-0410-9af5-da40c76e7ee4