net/mlx5: fix metadata item validation for ingress flows

net/mlx5: fix metadata item validation for ingress flows

In legacy metadata mode the metadata register B is engaged to
handle the metadata item. In the ingress domain the hardware
supports the register setting only, the match on register B
is not supported.

Due to this limitation only the SET_META action can be supported
for the ingress flows, the META item should be rejected on
flow validation.

Fixes: 5f3541724e08 ("net/mlx5: fix flow META item validation")
Cc: stable@dpdk.org
Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>