ixgbe: Don't reset the hardware when switching between LFC and PFC

When running in DCB mode, switching between link flow control and priority
flow control shouldn't need to reset the hardware.  This removes that
reset.

This also extends the set_all() dcbnl callback to return a value indicating
that the HW config changed, however a reset was not required.

Signed-off-by: Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>