Allow brAddTap to create a tap device that is down

An upcoming patch has a use for a tap device to be created that
doesn't need to be actually put into the "up" state, and keeping it
"down" keeps the output of ifconfig from being unnecessarily cluttered
(ifconfig won't show down interfaces unless you add "-a").

bridge.[ch]: add "up" as an arg to brAddTap()
uml_conf.c, qemu_command.c: add "up" (set to "true") to brAddTap() call.

src/qemu/qemu_command.c

@@ -252,6 +252,7 @@ qemuNetworkIfaceConnect(virConnectPtr conn,
                         &net->ifname,
                         tapmac,
                         vnet_hdr,
+                        true,
                         &tapfd))) {
         if (err == ENOTSUP) {
             /* In this particular case, give a better diagnostic. */

src/uml/uml_conf.c

@@ -143,6 +143,7 @@ umlConnectTapDevice(virConnectPtr conn,
                         &net->ifname,
                         tapmac,
                         0,
+                        true,
                         NULL))) {
         if (err == ENOTSUP) {
             /* In this particular case, give a better diagnostic. */

src/util/bridge.c

@@ -484,6 +484,7 @@ brAddTap(brControl *ctl,
          char **ifname,
          const unsigned char *macaddr,
          int vnet_hdr,
+         bool up,
          int *tapfd)
 {
     int fd;
@@ -530,7 +531,7 @@ brAddTap(brControl *ctl,
         goto error;
     if ((errno = brAddInterface(ctl, bridge, ifr.ifr_name)))
         goto error;
-    if ((errno = brSetInterfaceUp(ctl, ifr.ifr_name, 1)))
+    if (up && ((errno = brSetInterfaceUp(ctl, ifr.ifr_name, 1))))
         goto error;
     if (!tapfd &&
         (errno = ioctl(fd, TUNSETPERSIST, 1)))

src/util/bridge.h

@@ -71,6 +71,7 @@ int     brAddTap                (brControl *ctl,
                                  char **ifname,
                                  const unsigned char *macaddr,
                                  int vnet_hdr,
+                                 bool up,
                                  int *tapfd);
 
 int     brDeleteTap             (brControl *ctl,