accommodate configuring --without-lxc --without-qemu

* configure.in: Enable internal WITH_BRIDGE support not just for LXC or
QEMU, but also for --with-network.  Russell Haering reported that
compilation failed when configured with --without-lxc --without-qemu.
Details: http://thread.gmane.org/gmane.comp.emulators.libvirt/11928
* src/bridge.h: Use #if WITH_BRIDGE, rather than currently-equivalent
"#if defined(WITH_QEMU) || defined(WITH_LXC)"

src/bridge.h

@@ -24,7 +24,7 @@
 
 #include <config.h>
 
-#if defined(WITH_QEMU) || defined(WITH_LXC)
+#if defined(WITH_BRIDGE)
 
 #include <net/if.h>
 #include <netinet/in.h>
@@ -101,6 +101,6 @@ int     brGetEnableSTP          (brControl *ctl,
                                  const char *bridge,
                                  int *enable);
 
-#endif /* WITH_QEMU || WITH_LXC */
+#endif /* WITH_BRIDGE */
 
 #endif /* __QEMUD_BRIDGE_H__ */