Revert "MINOR: queue: make pendconn_first() take the lock by itself"

Revert "MINOR: queue: make pendconn_first() take the lock by itself"

This reverts commit 772e968b06f9348afea7f5785c97214a84c75d19.

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.