MarkerManager now logs every 10s how many marker datagrams the UDP sink
processed and the current throughput rate (match/s), so operators can
tell at a glance whether the single sink keeps up with the aggregated
uBridge traffic. Error count is also logged.
1000+ uBridge processes share a single UDP marker.sink endpoint. The
default kernel receive buffer (~208 KB) holds ~1000 datagrams — a
traffic burst can overflow it before the event loop drains them. Grow
it to 8 MB via setsockopt(SO_RCVBUF) so the kernel absorbs bursts
without silent packet loss. UDP is unordered — buffer size does not
affect per-datagram latency, only burst-loss resilience.
When the configured marker_listen_port (default 3070) is already in
use, fall back to an OS-assigned port instead of crashing the server.
If even port 0 fails, log the error and continue without marker
signals — traffic insight degrades rather than taking down startup.
