qemu serial: lost tx irqs (affecting FreeBSD's new uart(4) driver)

Well one problem seems to be the rx condition,
        ... if ((s->ier & UART_IER_RDI) && (s->lsr & UART_LSR_DR))
is not enough to trigger an irq, yet still causes the following
conditions not to be checked anymore at all.
Signed-off-by: NJuergen Lock <nox@jelal.kn-bremen.de>
Acked-by: NJan Kiszka <jan.kiszka@web.de>
Acked-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: NAurelien Jarno <aurelien@aurel32.net>

hw/serial.c

@@ -197,12 +197,10 @@ static void serial_update_irq(SerialState *s)
          * this is not in the specification but is observed on existing
          * hardware.  */
         tmp_iir = UART_IIR_CTI;
-    } else if ((s->ier & UART_IER_RDI) && (s->lsr & UART_LSR_DR)) {
-        if (!(s->fcr & UART_FCR_FE)) {
-           tmp_iir = UART_IIR_RDI;
-        } else if (s->recv_fifo.count >= s->recv_fifo.itl) {
-           tmp_iir = UART_IIR_RDI;
-        }
+    } else if ((s->ier & UART_IER_RDI) && (s->lsr & UART_LSR_DR) &&
+               (!(s->fcr & UART_FCR_FE) ||
+                s->recv_fifo.count >= s->recv_fifo.itl)) {
+        tmp_iir = UART_IIR_RDI;
     } else if ((s->ier & UART_IER_THRI) && s->thr_ipending) {
         tmp_iir = UART_IIR_THRI;
     } else if ((s->ier & UART_IER_MSI) && (s->msr & UART_MSR_ANY_DELTA)) {