Strip socket options on cross-cscf repeat listens (v0.7.2)

Make the shared-listen-include pattern work with `reuseport` and the
other socket-level listen options. Nginx core enforces at-most-once
per sockaddr on options that set lsopt.set=1 (reuseport, bind,
backlog=, rcvbuf=, sndbuf=, setfib=, fastopen=, accept_filter=,
deferred, ipv6only=, so_keepalive=) and emits "duplicate listen
options for <addr>" otherwise. That rule collides with a single
listens.conf included from every vhost — each vhost's include
re-submits the same options.

The listen wrapper now detects the cross-cscf case, strips those
options from cf->args before delegating to the core handler, and
logs one notice per stripped listen. The first cscf owns the
options on the kernel socket; later cscfs merge cleanly via
ngx_http_add_server. Protocol-level flags (ssl, http2, quic,
proxy_protocol) pass through untouched since nginx OR-merges those
across cscfs.

This unblocks `reuseport` for deployments that want better
new-connection spread across workers.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

debian/changelog

@@ -1,3 +1,23 @@
+nginx-ipng-stats-plugin (0.7.2-1) unstable; urgency=medium
+
+  * Pre-release v0.7.2.
+    - Listen wrapper now strips socket-level options (reuseport,
+      bind, backlog=, rcvbuf=, sndbuf=, setfib=, fastopen=,
+      accept_filter=, deferred, ipv6only=, so_keepalive=) from
+      cf->args when a sockaddr recurs under a different server
+      block. Previously this pattern — typical with a shared
+      `include listens.conf;` across vhosts — tripped nginx's
+      "duplicate listen options for <addr>" check because those
+      options are one-shot per kernel socket. The first cscf now
+      owns the options on the shared kernel socket and later
+      cscfs merge cleanly via ngx_http_add_server. A NOTICE is
+      logged each time socket options are stripped. This makes
+      `reuseport` usable with the shared-include deployment
+      pattern from docs/user-guide.md, which helps worker
+      load-balancing on busy hosts.
+
+ -- Pim van Pelt <pim@ipng.ch>  Sun, 19 Apr 2026 16:30:00 +0200
+
 nginx-ipng-stats-plugin (0.7.1-1) unstable; urgency=medium
 
   * Pre-release v0.7.1.