net/mlx5: eliminate dependency on Linux in shared header

net/mlx5: eliminate dependency on Linux in shared header

This commit eliminates Linux dependencies in shared file mlx5.h.

1. All functions using 'struct ifreq' are moved to file
linux/mlx5_ethdev_os.c such that this struct can be removed from mlx5.h.
2. Function mlx5_set_flags() that uses Linux flags (e.g. IFF_UP) is
changed to static and its prototype is removed from mlx5.h.
3. Remove redundant member verbs_action from 'struct mlx5_priv'.

Signed-off-by: Ophir Munk <ophirmu@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>