Summary: Allow for same vlan num on different physical NICs

Detail: A previous bug in the database schema did not allow the same vlan num
to exist on separate physical networks, even though this is possible and should
be allowed. To fix this, the code was changed to also disallow the same vlan
num on different physical networks, to avoid hitting the database constraint.
The database constraint has now been changed to allow only one of a vlan num
per physical nic per data center, so different physical nics can reuse vlan
numbers. This fix adjusts the code to match by removing the old fix.

BUG-ID: CLOUDSTACK-686
Signed-off-by: Marcus Sorensen <marcus@betterservers.com> 1358881555 -0700