Add ability to manipulate MACs

Special care is taken for bondethernet, where the MAC changes when
the first member is added to it. BondEthernet requires its MAC to
be set in the bondethernets section, disallowing the MAC of individual
members to be set.

Also write a dumper for MACs of all types. Update integration test
cases to stress the MAC changes on loops, bonds, and phys.

intest/intest.sh

@@ -25,5 +25,9 @@
   
       echo " - Checking that from $j to $j is empty"
       ../vppcfg plan -s ../schema.yaml -c $j -o /tmp/vppcfg-exec_${j}_${j}_null
+      [ -s /tmp/vppcfg-exec_${j}_${j}_null ] && {
+	  echo " - ERROR Transition is not empty"
+          cat /tmp/vppcfg-exec_${j}_${j}_null
+      }
     done
   done