ixgbe: fix namespace issues when FCoE/DCB is not enabled

Resolve namespace issues when FCoE or DCB is not enabled.
The issue is with certain configurations we end up with namespace
problems. A simple example:

ixgbe_main.c
 - defines func A()
 - uses func A()

ixgbe_fcoe.c
 - uses func A()

ixgbe.h
 - has prototype for func A()

For default (FCoE included) all is good.  But when it isn't the namespace
checker complains about how func A() could be static.

To resolve this, created a ixgbe_lib file to contain functions used
by DCB/FCoE and their helper functions so that they are always in
namespace whether or not DCB/FCoE is enabled.

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>