pci: Add root bus parameter to pci_nic_init()

At present, pci_nic_init() and pci_nic_init_nofail() assume that they will
only create a NIC under the primary PCI root.  As we add support for
multiple PCI roots, that may no longer be the case.  This patch adds a root
bus parameter to pci_nic_init() (and updates callers accordingly) to allow
the machine init code using it to specify the right PCI root for NICs
created by old-style -net nic parameters.  NICs created new-style, with
-device can of course be put anywhere.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
diff --git a/hw/arm/realview.c b/hw/arm/realview.c
index d6f47bf..036a188 100644
--- a/hw/arm/realview.c
+++ b/hw/arm/realview.c
@@ -59,7 +59,7 @@
     qemu_irq *irqp;
     qemu_irq pic[64];
     qemu_irq mmc_irq[2];
-    PCIBus *pci_bus;
+    PCIBus *pci_bus = NULL;
     NICInfo *nd;
     i2c_bus *i2c;
     int n;
@@ -250,7 +250,9 @@
             }
             done_nic = 1;
         } else {
-            pci_nic_init_nofail(nd, "rtl8139", NULL);
+            if (pci_bus) {
+                pci_nic_init_nofail(nd, pci_bus, "rtl8139", NULL);
+            }
         }
     }