[OPTIM] sepoll: do not re-check whole list upon accepts

[OPTIM] sepoll: do not re-check whole list upon accepts

There is already an optimisation in the speculative poller which
causes newly created FDs to be checked immediately after being
created. Unfortunately, this optimisation causes the whole spec
list to be re-checked while we're only interested in the new FDs.

Doing this minor change causes performance gains of up to 6% on
medium-sized objects with a few hundreds concurrent connections.