Fix build on Mingw32 wrt export of virNetServerGetDBusConn

Mingw32 complains if you request export of a symbol which does
not in fact exist.

* src/libvirt_bridge.syms, src/libvirt_macvtap.syms: Delete
  obsolete files
* src/libvirt_private.syms: Remove virNetServerGetDBusConn
* src/libvirt_dbus.syms: Add virNetServerGetDBusConn

src/Makefile.am

@@ -1175,16 +1175,12 @@ if WITH_DRIVER_MODULES
 USED_SYM_FILES += libvirt_driver_modules.syms
 endif
 
-if WITH_BRIDGE
-USED_SYM_FILES += libvirt_bridge.syms
-endif
-
 if WITH_LINUX
 USED_SYM_FILES += libvirt_linux.syms
 endif
 
-if WITH_MACVTAP
-USED_SYM_FILES += libvirt_macvtap.syms
+if HAVE_DBUS
+USED_SYM_FILES += libvirt_dbus.syms
 endif
 
 if WITH_LIBVIRTD

src/libvirt_bridge.syms

-#
-# These symbols are dependent upon --with-qemu or --with-lxc via
-# WITH_BRIDGE.
-#
-
-
-# bridge.h
-brAddBridge;
-brAddInetAddress;
-brAddInterface;
-brAddTap;
-brCreateTap;
-brDelInetAddress;
-brDeleteBridge;
-brDeleteTap;
-brHasBridge;
-brInit;
-brSetEnableSTP;
-brSetForwardDelay;
-brSetInetNetmask;
-brSetInterfaceMac;
-brSetInterfaceUp;
-brShutdown;

src/libvirt_dbus.syms

+# virnetserver.h
+virNetServerGetDBusConn;

src/libvirt_macvtap.syms

-#
-# These symbols are dependent on WITH_MACVTAP.
-#
-
-
-# macvtap.h
-delMacvtap;
-openMacvtapTap;
-vpAssociatePortProfileId;
-vpDisassociatePortProfileId;

src/libvirt_private.syms

@@ -1252,7 +1252,6 @@ virNetServerAddSignalHandler;
 virNetServerAutoShutdown;
 virNetServerClose;
 virNetServerFree;
-virNetServerGetDBusConn;
 virNetServerIsPrivileged;
 virNetServerNew;
 virNetServerQuit;