list: Define new API virConnectListAllNetworks

list: Define new API virConnectListAllNetworks

This is to list the network objects, supported filtering flags
are: active|inactive, persistent|transient, autostart|no-autostart.

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