usb: Remove magic constants from device bmAttributes

Replace magic constants in device bmAttributes with symbolic ones
from Linux kernel ch9.h

Signed-off-by: Pantelis Koukousoulas <pktoss@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/hw/usb/dev-network.c b/hw/usb/dev-network.c
index 4c532b7..d3fadbe 100644
--- a/hw/usb/dev-network.c
+++ b/hw/usb/dev-network.c
@@ -266,7 +266,7 @@
             .bNumInterfaces        = 2,
             .bConfigurationValue   = DEV_RNDIS_CONFIG_VALUE,
             .iConfiguration        = STRING_RNDIS,
-            .bmAttributes          = 0xc0,
+            .bmAttributes          = USB_CFG_ATT_ONE | USB_CFG_ATT_SELFPOWER,
             .bMaxPower             = 0x32,
             .nif = ARRAY_SIZE(desc_iface_rndis),
             .ifs = desc_iface_rndis,
@@ -274,7 +274,7 @@
             .bNumInterfaces        = 2,
             .bConfigurationValue   = DEV_CONFIG_VALUE,
             .iConfiguration        = STRING_CDC,
-            .bmAttributes          = 0xc0,
+            .bmAttributes          = USB_CFG_ATT_ONE | USB_CFG_ATT_SELFPOWER,
             .bMaxPower             = 0x32,
             .nif = ARRAY_SIZE(desc_iface_cdc),
             .ifs = desc_iface_cdc,