Currently, if the SNP driver for whatever reason fails to enable
receive filters for multicast frames, it falls back to enabling just
unicast and broadcast filters.  This breaks some IPv6 functionality as
the network card does not respond to neighbour solicitation requests.

Some cards refuse to enable EFI_SIMPLE_NETWORK_RECEIVE_MULTICAST, but
do support enabling EFI_SIMPLE_NETWORK_RECEIVE_PROMISCUOUS_MULTICAST,
so try it before falling back to just unicast+broadcast.

Signed-off-by: Ignat Korchagin <ignat@cloudflare.com>
Split-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>