igc: Fix IGC_MAX_RXNFC_RULES

IGC supports a total of 32 rules. 16 MAC address based, 8 VLAN priority
based, and 8 Ethertype based. This patch fixes IGC_MAX_RXNFC_RULES
accordingly.

Signed-off-by: Andre Guedes <andre.guedes@intel.com>
Acked-by: Sasha Neftin <sasha.neftin@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>