ipmi: disable IRQ and ATN on an external disconnect

Otherwise there's no way to clear them without an external command,
and it could lock the OS in the VM if they were stuck.

Signed-off-by: Corey Minyard <cminyard@mvista.com>

hw/ipmi/ipmi_bmc_extern.c

@@ -425,6 +425,11 @@ static void chr_event(void *opaque, int event)
             return;
         }
         ibe->connected = false;
+        /*
+         * Don't hang the OS trying to handle the ATN bit, other end will
+         * resend on a reconnect.
+         */
+        k->set_atn(s, 0, 0);
         if (ibe->waiting_rsp) {
             ibe->waiting_rsp = false;
             ibe->inbuf[1] = ibe->outbuf[1] | 0x04;