doc: tls: socket needs to be established to enable ulp

To enable TLS ulp socket needs to be in established state.
This was added in commit d91c3e17f7 ("net/tls: Only attach
to sockets in ESTABLISHED state"), in 2018.

Signed-off-by: Ulrich Weber <ulrich.weber@gmail.com>
Link: https://patch.msgid.link/20250626145618.15464-1-ulrich.weber@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Documentation/networking/tls.rst

@@ -16,11 +16,13 @@ User interface
 Creating a TLS connection
 -------------------------
 
-First create a new TCP socket and set the TLS ULP.
+First create a new TCP socket and once the connection is established set the
+TLS ULP.
 
 .. code-block:: c
 
   sock = socket(AF_INET, SOCK_STREAM, 0);
+  connect(sock, addr, addrlen);
   setsockopt(sock, SOL_TCP, TCP_ULP, "tls", sizeof("tls"));
 
 Setting the TLS ULP allows us to set/get TLS socket options. Currently