net/mlx5e: Ethtool link speed setting fixes

- Port speed settings are applied by the device only upon
  port admin status transition from DOWN to UP.
  So we enforce this transition regardless of the port's
  current operation state (which may be occasionally DOWN if
  for example the network cable is disconnected).
- Fix the PORT_UP/DOWN device interface enum
- Set the local_port bit in the device PAOS register
- EXPORT the PAOS (Port Administrative and Operational Status)
  register set/query access functions.

Signed-off-by: Achiad Shochat <achiad@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>