Wrong API Reference - Metering of Networking API V2

As Anne suggested, add "/metering" at line 16.
All the metering API here is not correct. Try on latest
neutron, they don't work. There is a "metering/" missing
in the URIs. Add it and try again, they all work.
Closes-bug: 1394489

Change-Id: If4c31b338afcffd965a0809e44991ee3daf447b0