rtl8139: use inline net_crc32() and bitshift instead of compute_mcast…

…_idx()

This makes it much easier to compare the multicast CRC calculation endian and
bitshift against the Linux driver implementation.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/net/rtl8139.c

@@ -882,7 +882,7 @@ static ssize_t rtl8139_do_receive(NetClientState *nc, const uint8_t *buf, size_t
                 return size;
             }
 
-            int mcast_idx = compute_mcast_idx(buf);
+            int mcast_idx = net_crc32(buf, ETH_ALEN) >> 26;
 
             if (!(s->mult[mcast_idx >> 3] & (1 << (mcast_idx & 7))))
             {