net/mlx4: fix default RSS hash fields

net/mlx4: fix default RSS hash fields

Using special types value -1 with mlx4_conv_rss_types() is supposed to
return a supported set of Verbs RSS hash fields, that is, priv->hw_rss_sup
unmodified.

Due to the way this function is written and because it is also used to
initially populate priv->hw_rss_sup however, this special value works
properly only once and fails with ENOTSUP errors afterward.

This problem can be seen when re-creating default flows (e.g. by entering
and leaving isolated mode).

Fixes: 024e87bef40b ("net/mlx4: restore UDP RSS by probing capabilities")
Cc: stable@dpdk.org
Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>