net/mlx5e: Activate HW multipath and handle port affinity based on FIB events

To support multipath offload we are going to track SW multipath route
and related nexthops. To do that we register to FIB notifier and handle
the route and next-hops events and reflect that as port affinity to HW.

When there is a new multipath route entry that all next-hops are the
ports of an HCA we will activate LAG in HW.

Egress wise, we use HW LAG as the means to emulate multipath on current
HW which doesn't support port selection based on xmit hash. In the
presence of multiple VFs which use multiple SQs (send queues) this
yields fairly good distribution.

HA wise, HW LAG buys us the ability for a given RQ (receive queue) to
receive traffic from both ports and for SQs to migrate xmitting over
the active port if their base port fails.

When the route entry is being updated to single path we will update
the HW port affinity to use that port only.

If a next-hop becomes dead we update the HW port affinity to the living
port.

When all next-hops are alive again we reset the affinity to default.

Due to FW/HW limitations, when a route is deleted we are not disabling
the HW LAG since doing so will not allow us to enable it again while
VFs are bounded. Typically this is just a temporary state when a
routing daemon removes dead routes and later adds them back as needed.

This patch only handles events for AF_INET.

Signed-off-by: Roi Dayan <roid@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>