docs: move the SIP guide into guide/network/

Change-Id: I3c2a7ea731d2fc3c0e2372e2f1a06ed659a6539f

Author: scottamain

docs/html/guide/guide_toc.cs

@@ -243,7 +243,7 @@ localized titles are added in the language order specified below.
       <li><a href="<?cs var:toroot?>guide/topics/wireless/bluetooth.html">
             <span class="en">Bluetooth</span>
           </a></li>
-       <li><a href="<?cs var:toroot?>guide/topics/sip/SIP.html">
+       <li><a href="<?cs var:toroot?>guide/topics/network/sip.html">
             <span class="en">Session Initiation Protocol</span></a>
             <span class="new">new!</span>
           </li>