net/mlx5e: Initialize all netdev common structures in one place

Move all mlx5e generic structures initializations to mlx5e_netdev_init.
The common structure new initializer function will be used to initialize
mlx5 context for netlink created netdevs such as IPoIB mlx5 accelerated
child netdevs.

Fixes: cd565b4b ("IB/IPoIB: Support acceleration options callbacks")
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Feras Daoud <ferasda@mellanox.com>