Potential bugs in flow entry management.

I found 2 potential bugs in flow entry management.

1. VTNFlow.isOutgoingNetwork(PortFilter, short) may return true unexpectedly
if the egress flow contains action that changes VLAN ID (POP_VLAN, SET_VLAN_ID).
This may cause the VTN Manager to uninstall unexpected flow entries.

2. MAC mapping should precede VLAN mapping. So when MAC mapping is activated,
VTN Manager needs to purge flow entries originated by VLAN mapping that
overlaps the MAC mapping. But currently VTN Manager purges flow entries
only if MAC mapping is activated by wildcard host entry.