doc/go1.16: document net TCP listener's backlog size update

Updates #41470

Change-Id: Iebd3a339504aa7f8834853d6a740557fb3bce3ef
Reviewed-on: https://go-review.googlesource.com/c/go/+/262938
Trust: Cuong Manh Le <[email protected]>
Trust: Emmanuel Odeke <[email protected]>
Run-TryBot: Cuong Manh Le <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Emmanuel Odeke <[email protected]>

Author: Cuong Manh Le

doc/go1.16.html

@@ -228,6 +228,12 @@ <h3 id="net"><a href="/pkg/net/">net</a></h3>
   with <code>"use of closed network connection"</code>.
 </p>
 
+<p><!-- CL 255898 -->
+  In previous Go releases the default TCP listener backlog size on Linux systems,
+  set by <code>/proc/sys/net/core/somaxconn</code>, was limited to a maximum of <code>65535</code>.
+  On Linux kernel version 4.1 and above, the maximum is now <code>4294967295</code>.
+</p>
+
 <h3 id="reflect"><a href="/pkg/reflect/">reflect</a></h3>
 
 <p><!-- CL 259237, golang.org/issue/22075 -->