net/mlx5: fix Tx meta width for modify field flow rule
net/mlx5: fix Tx meta width for modify field flow rule

Register C is used for the metadata within NIC Rx domain.
And its width can vary from 0 to 32 bits depending on
its kernel usage. But it is not the case within NIC Tx domain,
register A is always 32 bits there. Fix metadata width detection
for the modify_field flow API within NIC Tx domain.

Fixes: 6d5735c1cba2 ("net/mlx5: fix meta register conversion for extensive mode")
Cc: stable@dpdk.org

Signed-off-by: Alexander Kozyrev <a103889f73a7af0066377584f3d0eb32f9983c2e@nvidia.com>
Acked-by: Viacheslav Ovsiienko <5b8db9bb93a9a9aefc8828f79604d1fe963a53dd@nvidia.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk