docs: minor fixes to domain interface documentation

A few examples for <interface> had a type='direct' interface with no
sub-elements. This is not allowed - a type='direct' interface must
have at least a source element. (Most likely the example was copied
from the type='user' or type='ethernet' examples - they *do* allow an
instance with no sub-elements).

There was also one place that mistakenly used %lt; ... %gt; instead of
&lt; ... &gt; (for some reason, I make that typo all the time).

docs/formatdomain.html.in

@@ -2364,7 +2364,6 @@
 <pre>
   ...
   &lt;devices&gt;
-    &lt;interface type='direct'/&gt;
     ...
     &lt;interface type='direct'&gt;
       &lt;source dev='eth0' mode='vepa'/&gt;
@@ -2413,7 +2412,6 @@
 <pre>
   ...
   &lt;devices&gt;
-    &lt;interface type='direct'/&gt;
     ...
     &lt;interface type='direct'&gt;
       &lt;source dev='eth0.2' mode='vepa'/&gt;
@@ -2441,7 +2439,6 @@
   <pre>
   ...
   &lt;devices&gt;
-    &lt;interface type='direct'/&gt;
     ...
     &lt;interface type='direct'&gt;
       &lt;source dev='eth0' mode='private'/&gt;
@@ -2462,7 +2459,7 @@
       passthrough, after first optionally setting the device's MAC
       address to the configured value, and associating the device with
       an 802.1Qgh capable switch using an optionally specified
-      %lt;virtualport%gt; element (see the examples of virtualport
+      &lt;virtualport&gt; element (see the examples of virtualport
       given above for type='direct' network devices). Note that - due
       to limitations in standard single-port PCI ethernet card driver
       design - only SR-IOV (Single Root I/O Virtualization) virtual