i40e: Able to add up to 16 MAC filters on an untrusted VF

This patch fixes the problem with the driver being able to add only 7
multicast MAC address filters instead of 16. The problem is fixed by
changing the maximum number of MAC address filters to 16+1+1 (two extra
are needed because the driver uses 1 for unicast MAC address and 1 for
broadcast).

Signed-off-by: Adam Ludkiewicz <adam.ludkiewicz@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>