net: smc91c111: flush packets on RCR register changes

The SOFT_RST or RXEN in the control register can be used as a condition
to unblock the net layer via can_receive(). So check for possible
flushes on RCR changes. This will drop all pending packets on soft
reset or disable which is the functional intent of the can_receive()
logic.

Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Tested-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Message-id: b114d4c96f4afbdaa15f1361d9c07e3021755915.1441873621.git.crosthwaite.peter@gmail.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

hw/net/smc91c111.c

@@ -331,6 +331,7 @@ static void smc91c111_writeb(void *opaque, hwaddr offset,
             if (s->rcr & RCR_SOFT_RST) {
                 smc91c111_reset(DEVICE(s));
             }
+            smc91c111_flush_queued_packets(s);
             return;
         case 10: case 11: /* RPCR */
             /* Ignored */