net/mlx4: add port parameter

net/mlx4: add port parameter

Most ConnectX-3 adapters expose two physical ports on a single PCI bus
address.

Add a new port parameter allowing the user to choose
either or both physical ports to be used by the application.

This parameter is used as follows:

Selecting only the second port:
   -w 00:00.0,port=1

Selecting both ports:
   -w 00:00.0,port=0,port=1

If no parameter is given, the default behavior is unchanged: all ports
are probed.

Signed-off-by: Gaetan Rivet <gaetan.rivet@6wind.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>