OPTIM: queue: decrement the nbpend and totpend counters outside of the lock

OPTIM: queue: decrement the nbpend and totpend counters outside of the lock

We don't need to do that inside the lock. However since the operation
used to be done in deep functions, we have to make it resurface closer
to visible parts. It remains reasonably self-contained in queue.c so
that's not that big of a deal. Some places (redistribute) could benefit
from a single operation for all counts at once. Others like
pendconn_process_next_strm() are still called with both locks held but
now it will be possible to change this.