Revert "MEDIUM: queue: use a dedicated lock for the queues"

Revert "MEDIUM: queue: use a dedicated lock for the queues"

This reverts commit fcb8bf8650ec6b5614d1b88db54f1200ebd96cbd.

The recent changes since 5304669e1 MEDIUM: queue: make
pendconn_process_next_strm() only return the pendconn opened a tiny race
condition between stream_free() and process_srv_queue(), as the pendconn
is accessed outside of the lock, possibly while it's being freed. A
different approach is required.