i40e: fix FW_LLDP flag on init

Using ethtool --set-priv-flags disable-fw-lldp <on/off> is persistent
across reboots/reloads so we need some mechanism in the driver to detect
if it's on or off on init so we can set the ethtool private flag
appropriately.  Without this, every time the driver is reloaded the flag
will default to off regardless of whether it's on or off in FW.

We detect this by first attempting to program DCB and if AQ fails
returning I40E_AQ_RC_EPERM, we know that LLDP is disabled in FW.

Signed-off-by: Alan Brady <alan.brady@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>