Fix wrong value description

`lbaas` should be `metering`.

Also fix typos: coma -> comma.

Change-Id: I6e4e5531001bcf455d0dc74926725600d0cc2b4d
Closes-Bug: #1361997

doc/admin-guide-cloud/networking/section_networking_config-agents.xml

@@ -440,7 +440,7 @@ interface_driver = neutron.agent.linux.interface.OVSInterfaceDriver</programlist
                         >neutron-server</systemitem>:</para>
                 <programlisting language="ini">service_plugins = metering</programlisting>
                 <para>If this option is already defined, add
-                    <literal>lbaas</literal> to the list, using a coma as
+                    <literal>metering</literal> to the list, using a comma as
                     separator. For example:</para>
                 <programlisting language="ini">service_plugins = router,metering</programlisting>
             </step>
@@ -485,7 +485,7 @@ interface_driver = neutron.agent.linux.interface.OVSInterfaceDriver</programlist
                     file:</para>
                 <programlisting language="ini">service_plugins = lbaas</programlisting>
                 <para>If this option is already defined, add
-                    <literal>lbaas</literal> to the list, using a coma as
+                    <literal>lbaas</literal> to the list, using a comma as
                     separator. For example:</para>
                 <programlisting language="ini">service_plugins = router,lbaas</programlisting>
             </step>