When the number of sessions reaches MAX_SESSIONS, which defaults
to 1,000, turn off TCP and SSL listening sockets to prevent new
connections. When the session count falls below a low watermark,
currently 90% of MAX_SESSIONS, the listening sockets will be re-opened.
Helps prevent DoS and limit open file usage.
Bug fix: do not start serving paused connections until the buffer
socket is sufficiently drained. Also, loop.
e2f4847632