dcb: Add ieee_dcb_delapp() and dcb op to delete app entry

Now that we allow multiple IEEE App entries we need a way
to remove specific entries. To do this add the ieee_dcb_delapp()
routine.

Additionaly drivers may need to remove the APP entry from
their firmware tables. Add dcb ops routine to handle this.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>