ftgmac100: fix multicast hash routine

Based on the multicast hash calculation of the FTGMAC100 Linux driver.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180530061711.23673-4-clg@kaod.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/net/ftgmac100.c

@@ -776,8 +776,8 @@ static int ftgmac100_filter(FTGMAC100State *s, const uint8_t *buf, size_t len)
                 return 0;
             }
 
-            /* TODO: this does not seem to work for ftgmac100 */
-            mcast_idx = net_crc32(buf, ETH_ALEN) >> 26;
+            mcast_idx = net_crc32_le(buf, ETH_ALEN);
+            mcast_idx = (~(mcast_idx >> 2)) & 0x3f;
             if (!(s->math[mcast_idx / 32] & (1 << (mcast_idx % 32)))) {
                 return 0;
             }