MEDIUM: queue: make pendconn_free() work on the stream instead

MEDIUM: queue: make pendconn_free() work on the stream instead

Now pendconn_free() takes a stream, checks that pend_pos is set, clears
it, and uses pendconn_unlink() to complete the job. It's cleaner and
centralizes all the bookkeeping work in pendconn_unlink() only and
ensures that there's a single place where the stream's position in the
queue is manipulated.