Add -netdev bridge capabilities

This patch adds the capability in libvirt to check if
-netdev bridge option is supported or not.

Signed-off-by: Richa Marwaha <rmarwah@linux.vnet.ibm.com>
Signed-off-by: Corey Bryant<coreyb@linux.vnet.ibm.com>

tests/qemuhelptest.c

@@ -754,7 +754,8 @@ mymain(void)
             QEMU_CAPS_IDE_CD,
             QEMU_CAPS_NO_USER_CONFIG,
             QEMU_CAPS_HDA_MICRO,
-            QEMU_CAPS_NEC_USB_XHCI);
+            QEMU_CAPS_NEC_USB_XHCI,
+            QEMU_CAPS_NETDEV_BRIDGE);
 
     return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
 }