ixgbe: DCB remove ixgbe_fcoe_getapp routine

Remove ixgbe_fcoe_getapp() and use the generic kernel
routine instead. Also add application priority to the
kernel maintained list on setapp so applications and
stacks can query the value.

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>