He plugin: Meter stats not reported the first time switch connects to controller

Meters statistics are not reported the first time a switch connects to controller.

To reproduce:

1) Install controller with openflow feature (e.g. odl-openflowplugin-flow-services-ui)
2) Bring a switch with meter capabilities (e.g. CPqD- Note it will take a little while for CPqD to connect)
3) Start wireshark for the OF channel. Observe meter stats requests are not being sent to switch.
4) If we push a meter, this gets correctly installed in switch but no stats get reported because of the above.

Workaround:

Disconnect and connect the switch, now the meter stats messages are being sent.

BR/Luis