BUG/MAJOR: queue: properly keep count of the queue length

BUG/MAJOR: queue: properly keep count of the queue length

The queue length was moved to its own variable in commit 583303c48
("MINOR: proxies/servers: Calculate queueslength and use it."), however a
few places were missed in pendconn_unlink() and assign_server_and_queue()
resulting in never decreasing counts on aborted streams. This was
reproduced when injecting more connections than the total backend
could stand in TCP mode and letting some of them time out in the
queue. No backport is needed, this is only 3.2.