doc/go1.22: correct the system call name used for zero-copy from net.TCPConn to net.UnixConn

For #58808

Change-Id: I9b27af30888aaaa9659387a32c57aaea136b1c3a
Reviewed-on: https://go-review.googlesource.com/c/go/+/549335
Reviewed-by: Damien Neil <[email protected]>
Reviewed-by: Michael Pratt <[email protected]>
Auto-Submit: Michael Pratt <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: panjf2000

doc/go1.22.html

@@ -616,7 +616,7 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
     <p><!-- https://go.dev/issue/58808 -->
       When <a href="/pkg/io#Copy"><code>io.Copy</code></a> copies
       from a <code>TCPConn</code> to a <code>UnixConn</code>,
-      it will now use Linux's <code>sendfile(2)</code> system call if possible,
+      it will now use Linux's <code>splice(2)</code> system call if possible,
       using the new method <a href="/pkg/net#TCPConn.WriteTo"><code>TCPConn.WriteTo</code></a>.
     </p>