net/mlx5e: Support RSS for GRE tunneled packets

Introduce a new flow table and indirect TIRs which are used to hash the
inner packet headers of GRE tunneled packets.

When a GRE tunneled packet is received, the TTC flow table will match
the new IPv4/6->GRE rules which will forward it to the inner TTC table.
The inner TTC is similar to its counterpart outer TTC table, but
matching the inner packet headers instead of the outer ones (and does
not include the new IPv4/6->GRE rules).
The new rules will not add steering hops since they are added to an
already existing flow group which will be matched regardless of this
patch. Non GRE traffic will not be affected.

The inner flow table will forward the packet to inner indirect TIRs
which hash the inner packet and thus result in RSS for the tunneled
packets.

Testing 8 TCP streams bandwidth over GRE:
System: Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz
NIC: Mellanox Technologies MT28800 Family [ConnectX-5 Ex]
Before: 21.3 Gbps (Single RQ)
Now   : 90.5 Gbps (RSS spread on 8 RQs)

Signed-off-by: Gal Pressman <galp@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>