mlxsw: Update module's settings when module is plugged in

Module temperature warning events are enabled for modules that have a
temperature sensor and configured according to the temperature
thresholds queried from the module.

When a module is unplugged we are guaranteed not to get temperature
warning events. However, when a module is plugged in we need to
potentially update its current settings (i.e., event enablement and
thresholds).

Register to port module plug/unplug events and update module's settings
upon plug in events.

Signed-off-by: Amit Cohen <amcohen@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>