net/mlx5e: Fix devlink port register sequence

If udevd is configured to rename interfaces according to persistent
naming rules and if a network interface has phys_port_name in sysfs,
its contents will be appended to the interface name.
However, register_netdev creates device in sysfs and if
devlink_port_register is called after that, there is a timeframe in
which udevd may read an empty phys_port_name value. The consequence is
that the interface will lose this suffix and its name will not be
really persistent.

The solution is to register the port before registering a netdev.

Fixes: c6acd629 ("net/mlx5e: Add support for devlink-port in non-representors mode")
Signed-off-by: Vladyslav Tarasiuk <vladyslavt@mellanox.com>
Reviewed-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>