net/mlx5e: More generic netdev management API

In preparation for mlx5e RDMA net_device support, here we generalize
mlx5e_attach/detach in a way that those functions will be agnostic
to link type.  For that we move ethernet specific NIC net device logic out
of those functions into {nic,rep}_{enable/disable} mlx5e NIC and
representor profiles callbacks.

Also some of the logic was moved only to NIC profile since it is not right
to have this logic for representor net device (e.g. set port MTU).

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Erez Shitrit <erezsh@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>