net/mlx5: Eswitch, enable RoCE loopback traffic

When in switchdev mode, we would like to treat loopback RoCE
traffic (on eswitch manager) as RDMA and not as regular
Ethernet traffic
In order to enable it we add flow steering rule that forward RoCE
loopback traffic to the HW RoCE filter (by adding allow rule).
In addition we add RoCE address in GID index 0, which will be
set in the RoCE loopback packet.

Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Acked-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>