ice-9 poll handles buffered io too

* libguile/poll.c (scm_primitive_poll): Account for buffered I/O.

* module/ice-9/poll.scm (poll): Adapt to call primitive-poll with the
  port vector too.

module/ice-9/poll.scm

@@ -172,4 +172,5 @@
 (define* (poll poll-set #:optional (timeout -1))
   (primitive-poll (pset-pollfds poll-set)
                   (poll-set-nfds poll-set)
+                  (pset-ports poll-set)
                   timeout))