net/enic: move arguments into struct

net/enic: move arguments into struct

There are many copy_item functions, all with the same arguments, which
makes it difficult to add/change arguments. Move the arguments into a
struct to help subsequent commits that will add/fix features. Also
remove self-explanatory verbose comments for these local functions.

These changes are purely mechanical and have no impact on
functionalities.

Signed-off-by: Hyong Youb Kim <hyonkim@cisco.com>