ixgbe: DCB, only reprogram HW if the FCoE priority is changed

ixgbe: DCB, only reprogram HW if the FCoE priority is changed

If the FCoE priority is not changing do not set the RESET and
APP_UPCHG bits. This causes unneeded HW resets and which can
cause unneeded LLDP frames and negotiations.

The current check is not sufficient because the FCoE priority
can change twice during a negotiation which results in the
bits being set. This occurs when the switch changes the
priority or when the link is reset with switches that do not
include the APP priority until after PFC has been negotiated.

This results in set_app being called with the local APP
priority. Then the negotiation completes and set_app
is called again with the peer APP priority. The check
fails so the device is reset and the above occurs again
resulting in an endless loop of resets.

By only resetting the device if the APP priority has really
changed we short circuit the loop.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>