file-xfer: make handle_status agnostic of channel-main
file-xfer: make handle_status agnostic of channel-main

This make possible to rename the function to
spice_file_transfer_task_handle_status as a handler for
VDAgentFileXferStatusMessage for a specific task.

This change is related to split SpiceFileTransferTask from
channel-main.

Acked-by: Pavel Grunt <fbda40b445316123f12a5a6bd7556918ea74f4bc@redhat.com>
Acked-by: Jonathon Jongsma <c7254805a17bd5c41e24c3a278fcbf3afcdfb0fa@redhat.com>

fgouget/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk