DOC: config: mention uid dependency on the tune.quic.socket-owner option

This option defaults to "connection" but is also dependent on the user
being allowed to bind the specified port. Since QUIC can easily run on
non-privileged ports, usually this is not a problem, but if bound to port
443 it will usually fail. Let's mention this.

(cherry picked from commit 4d5f7d94b97aa0cc7153ab0b39b43c81f4024e51)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 8d9e74a..bf339f1 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -3382,7 +3382,9 @@
   and cases of transient errors during sendto() operation are handled
   efficiently. However, this relies on some advanced features from the UDP
   network stack. If your platform is deemed not compatible, haproxy will
-  automatically switch to "listener" mode on startup.
+  automatically switch to "listener" mode on startup. Please note that QUIC
+  listeners running on privileged ports may require to run as uid 0, or some
+  OS-specific tuning to permit the target uid to bind such ports.
 
   The "listener" value indicates that QUIC transfers will occur on the shared
   listener socket. This option can be a good compromise for small traffic as it