eepro100: Fix multicast regression

Commit 7fc8d918 removed code from
eepro100.c and replaced it by different code: the code in net.c
returns bits 31...26, but eepro100 needs bits 7...2.

This patch partially reverts 7fc8d918.
To avoid future problems, I renamed the function and changed the comment.
Signed-off-by: NStefan Weil <sw@weilnetz.de>
Acked-by: NJason Wang <jasowang@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/eepro100.c

@@ -322,8 +322,32 @@ static const uint16_t eepro100_mdi_mask[] = {
     0xffff, 0xffff, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000, 0x0000,
 };
 
+#define POLYNOMIAL 0x04c11db6
+
 static E100PCIDeviceInfo *eepro100_get_class(EEPRO100State *s);
 
+/* From FreeBSD (locally modified). */
+static unsigned e100_compute_mcast_idx(const uint8_t *ep)
+{
+    uint32_t crc;
+    int carry, i, j;
+    uint8_t b;
+
+    crc = 0xffffffff;
+    for (i = 0; i < 6; i++) {
+        b = *ep++;
+        for (j = 0; j < 8; j++) {
+            carry = ((crc & 0x80000000L) ? 1 : 0) ^ (b & 0x01);
+            crc <<= 1;
+            b >>= 1;
+            if (carry) {
+                crc = ((crc ^ POLYNOMIAL) | carry);
+            }
+        }
+    }
+    return (crc & BITS(7, 2)) >> 2;
+}
+
 /* Read a 16 bit control/status (CSR) register. */
 static uint16_t e100_read_reg2(EEPRO100State *s, E100RegisterOffset addr)
 {
@@ -823,7 +847,7 @@ static void set_multicast_list(EEPRO100State *s)
         uint8_t multicast_addr[6];
         pci_dma_read(&s->dev, s->cb_address + 10 + i, multicast_addr, 6);
         TRACE(OTHER, logout("multicast entry %s\n", nic_dump(multicast_addr, 6)));
-        unsigned mcast_idx = compute_mcast_idx(multicast_addr);
+        unsigned mcast_idx = e100_compute_mcast_idx(multicast_addr);
         assert(mcast_idx < 64);
         s->mult[mcast_idx >> 3] |= (1 << (mcast_idx & 7));
     }
@@ -1650,7 +1674,7 @@ static ssize_t nic_receive(VLANClientState *nc, const uint8_t * buf, size_t size
         if (s->configuration[21] & BIT(3)) {
           /* Multicast all bit is set, receive all multicast frames. */
         } else {
-          unsigned mcast_idx = compute_mcast_idx(buf);
+          unsigned mcast_idx = e100_compute_mcast_idx(buf);
           assert(mcast_idx < 64);
           if (s->mult[mcast_idx >> 3] & (1 << (mcast_idx & 7))) {
             /* Multicast frame is allowed in hash table. */