Fix the low level OVS driver to really do egress

Fix the low level OVS driver to really do egress

It seems that the Queue + QoS + linux-htb implementation was really
limiting ingress by default. So this patch switches the implementation
to the ovs ingress_policing_rate and ingress_policing_burst parameters
of the Interface table.

Later in time we may want to revise this, to make TC & queueing possible,
but this is good enough for egress limiting.

Also, removed the _update_bandwidth_limit del+set on OvS QoS driver for
the bandwidth limit rule update, since that's not needed anymore.

Change-Id: Ie802a235ae19bf679ba638563ac7377337448f2a
Partially-Implements: ml2-qos