net/mlx4_core: Load higher level modules according to ports type

Mellanox ConnectX architecture is:  mlx4_core is the lower level
PCI driver which register on the PCI id, and protocol specific drivers
are depended on it: mlx4_en - for Ethernet and mlx4_ib for Infiniband.
NIC could have multiple ports which can change their type dynamically.
We use the request_module() call to load the relevant protocol driver
when needed: on loading time or at port type change event.

Signed-off-by: Eyal Perry <eyalpe@mellanox.com>
Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>