net/mlx5: fix count in xstats
net/mlx5: fix count in xstats

With the commit af4f09f28294 ("net/mlx5: prefix all functions with mlx5"),
mlx5_xstats_get() is not compliant any longer with the api.
It always returns the caller max entries count while it should return how
many entries it wrote/wanted to write.

Fixes: af4f09f28294 ("net/mlx5: prefix all functions with mlx5")

Signed-off-by: David Marchand <f28529695cfa9e3e1eb84e7072aa626af4abb18e@6wind.com>
Acked-by: Nelio Laranjeiro <2f8dd9032d5b85ca4b53dec8ce664eb6998836be@6wind.com>

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