net/mlx5: fix call to modify action without init item

net/mlx5: fix call to modify action without init item

The item is being set according to the attribute value, whether it is
udp/tcp or ipv4/6.
Also, there are two condition calls.

If the attribute is neither udp/tcp or ipv4/6 the item is not
initialized at all, but the call to the flow_dv_convert_modify_action is
still being done.
Also, even if the attribute is tcp/udp or ipv4/6, we still have two
conditions.

This patch changes the conditions, so the item will always be set.
By doing this, there is also a save in the number of condition calls.

Fixes: 4bb14c83df95 ("net/mlx5: support modify header using Direct Verbs")
Cc: stable@dpdk.org
Signed-off-by: Asaf Penso <asafp@mellanox.com>
Reviewed-by: Dekel Peled <dekelp@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>