list: Define new API virConnectListAllNWFilters

This is to list the network filter objects. No flags are supported

include/libvirt/libvirt.h.in: Declare enum virConnectListAllNWFilterFlags
                              and virConnectListAllNWFilters.
python/generator.py: Skip auto-generating
src/driver.h: (virDrvConnectListAllNWFilters)
src/libvirt.c: Implement the public API
src/libvirt_public.syms: Export the symbol to public

include/libvirt/libvirt.h.in

@@ -4126,7 +4126,9 @@ int                     virConnectNumOfNWFilters (virConnectPtr conn);
 int                     virConnectListNWFilters  (virConnectPtr conn,
                                                   char **const names,
                                                   int maxnames);
-
+int                     virConnectListAllNWFilters(virConnectPtr conn,
+                                                   virNWFilterPtr **filters,
+                                                   unsigned int flags);
 /*
  * Lookup nwfilter by name or uuid
  */