This is most efficient (kernel knows what's available) & cleaner.

Of course, this is not perfect either. Still, it solved many "port already
in use" happening for me with previous implementation, for some reason.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2372 71dcc9de-d417-0410-9af5-da40c76e7ee4