ixgbe: Read and parse NW_MNG_IF_SEL register

Read the IXGBE_NW_MNG_IF_SEL register and use it to set interface
attributes.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>