node_device: Expose link state & speed

While exposing the info under <interface/> in previous patch works, it
may work only in cases where interface is configured on the host.
However, orchestrating application may want to know the link state and
speed even in that case. That's why we ought to expose this in nodedev
XML too:

virsh # nodedev-dumpxml net_eth0_f0_de_f1_2b_1b_f3
<device>
  <name>net_eth0_f0_de_f1_2b_1b_f3</name>
  <path>/sys/devices/pci0000:00/0000:00:19.0/net/eth0</path>
  <parent>pci_0000_00_19_0</parent>
  <capability type='net'>
    <interface>eth0</interface>
    <address>f0🇩🇪f1:2b:1b:f3</address>
    <link speed='1000' state='up'/>
    <capability type='80203'/>
  </capability>
</device>

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

docs/formatnode.html.in

@@ -161,6 +161,13 @@
               <dd>The interface name tied to this device.</dd>
               <dt><code>address</code></dt>
               <dd>If present, the MAC address of the device.</dd>
+              <dt><code>link</code></dt>
+              <dd>Optional to reflect the status of the link. It has
+                two optional attributes: <code>speed</code> in Mbits per
+                second and <code>state</code> to tell the state of the
+                link. So far, the whole element is just for output,
+                not setting.
+              </dd>
               <dt><code>capability</code></dt>
               <dd>A network protocol exposed by the device, where the
                 attribute <code>type</code> can be "80203" for IEEE

docs/schemas/nodedev.rng

@@ -243,6 +243,7 @@
         <ref name='mac'/>
       </element>
     </optional>
+    <ref name="link-speed-state"/>
 
     <zeroOrMore>
       <ref name='subcapnet'/>