when retrieving elanService.getExternalElanInterfaces for router port's external network, we get an additional dummy external interface (besides the actual ones). For example: 0:eth1:flat. This external interface has no state and therefore causes an NPE (in both FloatingIpGarpHandler and NeutronSubnetGwMacResolver):

2016-08-23 18:11:30,472 | ERROR | Gw-Mac-Res | InterfaceManagerRpcService | 318 - org.opendaylight.genius.interfacemanager-impl - 0.1.0.SNAPSHOT | Retrieval of lport tag for the key 0:eth1:flat failed due to java.lang.NullPointerException

2016-08-23 18:11:30,485 | ERROR | pool-45-thread-1 | InterfaceManagerRpcService | 318 - org.opendaylight.genius.interfacemanager-impl - 0.1.0.SNAPSHOT | Retrieval of datapath id for the key 0:eth1:flat failed due to java.lang.NullPointerException