net:ethernet:aquantia: Fix for multicast filter handling.

Since the HW supports up to 32 multicast filters we should
track count of multicast filters to avoid overflow.
If we attempt to add >32 multicast filter - just set NETIF_ALLMULTI flag
instead.

Fixes: 94f6c9e4cdf6 ("net: ethernet: aquantia: Support for NIC-specific code")
Signed-off-by: Igor Russkikh <Igor.Russkikh@aquantia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>