net/mlx5: fix modify field action order for MAC

net/mlx5: fix modify field action order for MAC

MAC addresses are split into 2 parts inside Mellanox NIC:
bits 0-15 are separate from bits 16-47. That makes a copy
from another packet field tricky because any other field
is aligned to 32 bits, not 16. This causes unexpected
results when using the MODIFY_FIELD action with MAC addresses.
Track crossing MAC addresses boundary and arrange a proper
order for the MODIFY_FIELD action involving MAC addresses.

Fixes: 641dbe4fb053 ("net/mlx5: support modify field flow action")
Cc: stable@dpdk.org
Signed-off-by: Alexander Kozyrev <akozyrev@nvidia.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>