dp8393x: Clear descriptor in_use field to release packet

When the SONIC receives a packet into the last available descriptor, it
retains ownership of that descriptor for as long as necessary.

Section 3.4.7 of the datasheet says,

    When the system appends more descriptors, the SONIC releases ownership
    of the descriptor after writing 0000h to the RXpkt.in_use field.

The packet can now be processed by the host, so raise a PKTRX interrupt,
just like the normal case.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Tested-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/net/dp8393x.c

@@ -811,7 +811,17 @@ static ssize_t dp8393x_receive(NetClientState *nc, const uint8_t * buf,
             return -1;
         }
         /* Link has been updated by host */
+
+        /* Clear in_use */
+        size = sizeof(uint16_t) * width;
+        address = dp8393x_crda(s) + sizeof(uint16_t) * 6 * width;
+        dp8393x_put(s, width, 0, 0);
+        address_space_rw(&s->as, address, MEMTXATTRS_UNSPECIFIED,
+                         (uint8_t *)s->data, size, 1);
+
+        /* Move to next descriptor */
         s->regs[SONIC_CRDA] = s->regs[SONIC_LLFA];
+        s->regs[SONIC_ISR] |= SONIC_ISR_PKTRX;
     }
 
     /* Save current position */