STEPS TO REPRODUCE. it's very simple.
Step 1. Create a Network(NET1), Subnet(SUBNET1) and 1 Port. and verify if table 50(SMAC) and 51(DMAC) is programmed fine.
Step 2. logout karaf and killall java process and delete data, journal and snapshot folders
Step 3. start karaf and feature:install netvirt-openstack
Step 4. Create a new port in network(NET1) --> NPE occurs

FYI:
1. Added multiple ports before Step 2. all were successfully added.
2. Setup i was working on is a docker setup, where i am creating tap ports via mininet and later setting interface id's like below
ovs-vsctl set Interface "tap23701c04-11" external_ids:iface-id='23701c04-1118-4c65-9425-78a80d49a218'
3. Logs after Step 4 attached.

2017-05-31 15:43:53,962 | WARN | eChangeHandler-0 | NeutronPortChangeListener | 365 - org.opendaylight.netvirt.neutronvpn-impl - 0.5.0.SNAPSHOT | neutron vpn received a port add() for a network without a provider extension augmentation or with an unsupported network type for the port 23701c04-1318-4c65-9425-78a80d49a218 which is part of network null
2017-05-31 15:43:54,023 | ERROR | eChangeHandler-0 | AsyncDataTreeChangeListenerBase | 320 - org.opendaylight.genius.mdsalutil-api - 0.3.0.SNAPSHOT | Thread terminated due to uncaught exception: AsyncDataTreeChangeListenerBase-DataTreeChangeHandler-0
java.lang.NullPointerException
at org.opendaylight.netvirt.qosservice.QosNeutronUtils.hasBandwidthLimitRule(QosNeutronUtils.java:831)[372:org.opendaylight.netvirt.qosservice-impl:0.5.0.SNAPSHOT]
at org.opendaylight.netvirt.qosservice.QosNeutronPortChangeListener.add(QosNeutronPortChangeListener.java:69)[372:org.opendaylight.netvirt.qosservice-impl:0.5.0.SNAPSHOT]
at org.opendaylight.netvirt.qosservice.QosNeutronPortChangeListener.add(QosNeutronPortChangeListener.java:28)[372:org.opendaylight.netvirt.qosservice-impl:0.5.0.SNAPSHOT]
at org.opendaylight.genius.datastoreutils.AsyncDataTreeChangeListenerBase$DataTreeChangeHandler.run(AsyncDataTreeChangeListenerBase.java:155)[320:org.opendaylight.genius.mdsalutil-api:0.3.0.SNAPSHOT]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)[:1.8.0_73]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)[:1.8.0_73]
at java.lang.Thread.run(Thread.java:745)[:1.8.0_73]