CLOUDSTACK-7903: Fix build regression from previous fix

The previous fix tried to access StatsCollector from UsageManagerImpl
which is not possible due to dependency cycle.

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>
(cherry picked from commit 1e0880cbabfb2c8edbd6a5a35b9417b2f3e6f681)
Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>

Conflicts:
	server/src/com/cloud/network/router/VirtualNetworkApplianceManagerImpl.java