net/mlx5e: Split offloaded eswitch TC rules for port mirroring

If a TC rule needs to be split for mirroring, create two HW rules,
in the first level and the second level flow tables accordingly.

In the first level flow table, forward the packet to the mirror
port and forward the packet to the second level flow table for
further processing, eg. encap, vlan push or header re-write.

Currently the matching is repeated in both stages.

While here, simplify the setup of the vhca id valid indicator also
in the existing code.

Signed-off-by: Chris Mi <chrism@mellanox.com>
Reviewed-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>