i40e: Prevent link flow control settings when PFC is enabled

When PFC is enabled we should not proceed with setting the link flow control
parameters.  Also, always report the link flow Tx/Rx settings as off when
PFC is enabled.

Change-ID: Ib09ec58afdf0b2e587ac9d8851a5c80ad58206c4
Signed-off-by: Neerav Parikh <neerav.parikh@intel.com>
Tested-By: Jack Morgan <jack.morgan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>