Simplify the mlx4 driver interface by removing mlx4_get_protocol_dev()
and the associated mlx4_interface.get_dev callbacks. This is done in
preparation to use an auxiliary bus to model the mlx4 driver structure.

The change is motivated by the following situation:
* The mlx4_en interface is being initialized by mlx4_en_add() and
  mlx4_en_activate().
* The latter activate function calls mlx4_en_init_netdev() ->
  register_netdev() to register a new net_device.
* A netdev event NETDEV_REGISTER is raised for the device.
* The netdev notififier mlx4_ib_netdev_event() is called and it invokes
  mlx4_ib_scan_netdevs() -> mlx4_get_protocol_dev() ->
  mlx4_en_get_netdev() [via mlx4_interface.get_dev].

This chain creates a problem when mlx4_en gets switched to be an
auxiliary driver. It contains two device calls which would both need to
take a respective device lock.

Avoid this situation by updating mlx4_ib_scan_netdevs() to no longer
call mlx4_get_protocol_dev() but instead to utilize the information
passed in net_device.parent and net_device.dev_port. This data is
sufficient to determine that an updated port is one that the mlx4_ib
driver should take care of and to keep mlx4_ib_dev.iboe.netdevs up to
date.

Following that, update mlx4_ib_get_netdev() to also not call
mlx4_get_protocol_dev() and instead scan all current netdevs to find
find a matching one. Note that mlx4_ib_get_netdev() is called early from
ib_register_device() and cannot use data tracked in
mlx4_ib_dev.iboe.netdevs which is not at that point yet set.

Finally, remove function mlx4_get_protocol_dev() and the
mlx4_interface.get_dev callbacks (only mlx4_en_get_netdev()) as they
became unused.
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Tested-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Acked-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>