Bug #24702: Fix PXE ROM size mismatch

For pc-0.14 and older use the PXE ROMs from the deprecated etherboot-qemu
package, which have different sizes. Without the patch the virtual PC gets
build with the current ROM sizes. Loading then fails because the stored PCI ROM
BAR size mismatches the configured size.
--- a/hw/pc_piix.c
+++ b/hw/pc_piix.c
@@ -433,6 +433,30 @@ static QEMUMachine pc_machine_v0_15 = {
             .driver   = "virtio-balloon-pci",\
             .property = "event_idx",\
             .value    = "off",\
+        },{\
+            .driver   = "ne2000",\
+            .property = "romfile",\
+            .value   = "/usr/lib/etherboot/rtl8029.rom",\
+        },{\
+            .driver   = "rtl8139",\
+            .property = "romfile",\
+            .value   = "/usr/lib/etherboot/rtl8139.rom",\
+        },{\
+            .driver   = "e1000",\
+            .property = "romfile",\
+            .value   = "/usr/lib/etherboot/e1000-82540em.rom",\
+        },{\
+            .driver   = "pcnet",\
+            .property = "romfile",\
+            .value   = "/usr/lib/etherboot/pcnet32.rom",\
+        },{\
+            .driver   = "ne2k-isa",\
+            .property = "romfile",\
+            .value   = "/usr/lib/etherboot/ne.rom",\
+        },{\
+            .driver   = "virtio-net-pci",\
+            .property = "romfile",\
+            .value   = "/usr/lib/etherboot/virtio-net.rom",\
         }
 
 static QEMUMachine pc_machine_v0_14 = {