Fix ipv4-addr definition in interface.rng

Eric Blake pointed out a deficiency in this regex when it was
copy-pasted into network.rng. This is just propogating the fix back to
its origin.

docs/schemas/interface.rng

@@ -439,7 +439,7 @@
 
   <define name='ipv4-addr'>
     <data type='string'>
-      <param name="pattern">(((25[0-5])|(1[0-9]{2})|(2[0-4][0-9])|([0-9]{1,2}))\.){3}((25[0-5])|(1[0-9]{2})|(2[0-4][0-9])|([0-9]{1,2}))</param>
+      <param name="pattern">(((25[0-5])|(2[0-4][0-9])|(1[0-9]{2})|([1-9][0-9])|([0-9]))\.){3}((25[0-5])|(2[0-4][0-9])|(1[0-9]{2})|([1-9][0-9])|([0-9]))</param>
     </data>
   </define>