This patch implements the L3 agent side router gateway IP rate
limit. For routers in centralized snat node (network node),
the tc rules will be set on the corresponding device in router
namespace:
1. Legacy and HA router, qrouter-namespace and qg-device
2. Dvr (edge) router, snat namespace and qg-device
If gateway IP rate limit was set, then under the same router,
all the VMs without floating IP will share the bandwidth.
Partially-Implements blueprint: router-gateway-ip-qos
Closes-Bug: #1757044
Change-Id: Ie92ff0d4df0e85ce71c7d50f34ea6ff973812af8
cd3cc7e908