restructure the code which adds support for configuring
PCIe VF via mgmt netdevice. which was added by
commit 7829451c ("cxgb4: Add control net_device for
configuring PCIe VF")

Original work by: Casey Leedom <leedom@chelsio.com>
Signed-off-by: NGanesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>