net/mlx5: fix CVLAN tag set in IP item translation

net/mlx5: fix CVLAN tag set in IP item translation

Previous fix added, at the end of functions
flow_dv_translate_item_ipv4() and flow_dv_translate_item_ipv6(), the
setting of cvlan_tag mask.
In the case of unspecified item (item->spec == null) these functions
return, and the new code section is not reached.

This patch moves the setting of cvlan_tag mask to be done before the
check of item->spec, to make sure it is always executed.

Fixes: 797329d6c4a1 ("net/mlx5: fix match on ethertype and CVLAN tag")
Cc: stable@dpdk.org
Signed-off-by: Dekel Peled <dekelp@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>