net/mlx4_en: Ignore irrelevant hypervisor events

MLX4_DEV_EVENT_SLAVE_INIT and MLX4_DEV_EVENT_SLAVE_SHUTDOWN
events used by Hypervisor to inform the PPF IB driver that
IB para-virtualization must be initialized/destroyed for a slave.
If this event is catched by ETH VF annoying but harmless error message
is printed into dmesg. Remove dmesg prints for these events.

Signed-off-by: Eugenia Emantayev <eugenia@mellanox.co.il>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>