Unlimited netmgr buffering is causing high memory usage under high load

The changed buffering of the inactive sockets and uvreqs in BIND 9.19 is keeping memory allocated for the sockets and buffers. This is not necessarily bad, but as we are using jemalloc that provides similar (generic) capability to cache small objects, we might as well explore the option to remove the caching.

The preliminary results show only a little dip in the performance: