Revert "xenserver: Make primary management interface on VLAN possible."

Revert "xenserver: Make primary management interface on VLAN possible."

This reverts commit d71cb7eb3e52fbf521abe6d0cb19cc8b7aea80dc.

The strategy used in that commit for making the primary management
interface on a VLAN possible did not work reliably.  Sometimes it would
work for a time, but eventually xapi would start listening only on the IP
address attached to the fake VLAN bridge.  Since this is not a real IP
address that can be used to talk to the outside world (and in any case it
isn't the IP address requested by the administrator) xapi would become
unreachable at this point.