ovn: Add the documentation for the DHCP opt 'wpad' in proper section

The commit "6f01617442" added the documenation for the DHCPv4 option
252 in the wrong section. This patch fixes it.

Fixes: 6f01617 ("ovn: Add DHCP support for option 252.")
Signed-off-by: Numan Siddique <nusiddiq@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Mark Michelson <mmichels@redhat.com>

ovn/ovn-nb.xml

@@ -1992,13 +1992,6 @@
           </p>
         </column>
 
-        <column name="options" key="wpad">
-          <p>
-            The DHCPv4 option code for this option is 252. This option is used
-            as part of web proxy auto discovery to provide a URL for a web
-            proxy.
-          </p>
-        </column>
       </group>
 
       <group title="Boolean DHCP Options">
@@ -2063,6 +2056,20 @@
           for this option is 59.
         </column>
       </group>
+
+      <group title="String DHCP Options">
+        <p>
+          These options accept a string value.
+        </p>
+
+        <column name="options" key="wpad">
+          <p>
+            The DHCPv4 option code for this option is 252. This option is used
+            as part of web proxy auto discovery to provide a URL for a web
+            proxy.
+          </p>
+        </column>
+      </group>
     </group>
 
     <group title="DHCPv6 options">