list: Implement RPC calls for virConnectListAllNWFilters

list: Implement RPC calls for virConnectListAllNWFilters

The RPC generator doesn't support returning list of object yet, this patch
do the work manually.

  * daemon/remote.c:
    Implemente the server side handler remoteDispatchConnectListAllNWFilters.

  * src/remote/remote_driver.c:
    Add remote driver handler remoteConnectListAllNWFilters.

  * src/remote/remote_protocol.x:
    New RPC procedure REMOTE_PROC_CONNECT_LIST_ALL_NWFILTERS and
    structs to represent the args and ret for it.

  * src/remote_protocol-structs: Likewise.