net/mlx5: improve flow item IP validation

net/mlx5: improve flow item IP validation

Currently PMD doesn't check whether the user specified ethernet type is
conflicting with the followed IPv4/IPv6 items, which leads to HW refuse
to create rule, for example:

  ... pattern eth type is 0x86dd / ipv4 / end ...

ethernet type is IPv6 but IPv4 is following, this should be validated
as failure and report corresponding error in detail.

Fixes: 23c1d42c7138 ("net/mlx5: split flow validation to dedicated function")
Cc: stable@dpdk.org
Signed-off-by: Xiaoyu Min <jackmin@mellanox.com>
Acked-by: Ori Kam <orika@mellanox.com>