CLOUDSTACK-5697 This patchset fixes a bug with the recently merged
vxlan code. Users can set a physical network to isolation type 'vxlan',
put public traffic on that physical network, and it will still attempt
to use 'vlan' isolation on the KVM hosts. This is going to be an issue
for other isolation types as well, but I'm not familiar with them, so
I'm just fixing vxlan for now.