net/mlx5: Handle "enable_roce" devlink param

Register "enable_roce" param, default value is RoCE enabled.
Current configuration is stored on mlx5_core_dev and exposed to user
through the cmode runtime devlink param.
Changing configuration requires changing the cmode driverinit devlink
param and calling devlink reload.

Signed-off-by: Michael Guralnik <michaelgur@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>