This feature is used to limit the bandwidth of flows, such as floating IP.

ovn-northd changes:
1. add bandwidth column in NB's QOS table.
2. add QOS_METER stages in Logical switch ingress/egress.
3. add set_meter() action in SB's LFlow table.

ovn-controller changes:
add meter_table for meter action process openflow meter table.

Now, This feature is only supported in DPDK.

Signed-off-by: Guoshuai Li <ligs@dtdream.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>