net/ark: allow unique user data for each port

net/ark: allow unique user data for each port

This change allows a user extension to provide unique private
callback data for all ports.

Arkville is a single-function multi-port device.  User_data resides
in the singleton Arkville structure.  This structure is shared across
all ports.

With this patch, we are providing a unique user pointer for each port
rather than a common pointer across multiple ports.

Signed-off-by: John Miller <john.miller@atomicrules.com>