revalidator: Rebalance offloaded flows based on the pps rate

This is the third patch in the patch-set to support dynamic rebalancing
of offloaded flows.

The dynamic rebalancing functionality is implemented in this patch. The
ukeys that are not scheduled for deletion are obtained and passed as input
to the rebalancing routine. The rebalancing is done in the context of
revalidation leader thread, after all other revalidator threads are
done with gathering rebalancing data for flows.

For each netdev that is in OOR state, a list of flows - both offloaded
and non-offloaded (pending) - is obtained using the ukeys. For each netdev
that is in OOR state, the flows are grouped and sorted into offloaded and
pending flows.  The offloaded flows are sorted in descending order of
pps-rate, while pending flows are sorted in ascending order of pps-rate.

The rebalancing is done in two phases. In the first phase, we try to
offload all pending flows and if that succeeds, the OOR state on the device
is cleared. If some (or none) of the pending flows could not be offloaded,
then we start replacing an offloaded flow that has a lower pps-rate than
a pending flow, until there are no more pending flows with a higher rate
than an offloaded flow. The flows that are replaced from the device are
added into kernel datapath.

A new OVS configuration parameter "offload-rebalance", is added to ovsdb.
The default value of this is "false". To enable this feature, set the
value of this parameter to "true", which provides packets-per-second
rate based policy to dynamically offload and un-offload flows.

Note: This option can be enabled only when 'hw-offload' policy is enabled.
It also requires 'tc-policy' to be set to 'skip_sw'; otherwise, flow
offload errors (specifically ENOSPC error this feature depends on) reported
by an offloaded device are supressed by TC-Flower kernel module.

Signed-off-by: Sriharsha Basavapatna <sriharsha.basavapatna@broadcom.com>
Co-authored-by: Venkat Duvvuru <venkatkumar.duvvuru@broadcom.com>
Signed-off-by: Venkat Duvvuru <venkatkumar.duvvuru@broadcom.com>
Reviewed-by: Sathya Perla <sathya.perla@broadcom.com>
Reviewed-by: Ben Pfaff <blp@ovn.org>
Signed-off-by: Simon Horman <simon.horman@netronome.com>

lib/netdev.h

@@ -230,6 +230,7 @@ int netdev_init_flow_api(struct netdev *);
 uint32_t netdev_get_block_id(struct netdev *);
 int netdev_get_hw_info(struct netdev *, int);
 void netdev_set_hw_info(struct netdev *, int, int);
+bool netdev_any_oor(void);
 bool netdev_is_flow_api_enabled(void);
 void netdev_set_flow_api_enabled(const struct smap *ovs_other_config);
 bool netdev_is_offload_rebalance_policy_enabled(void);