dfu: Support download of large DFU firmware
dfu: Support download of large DFU firmware

The nr_chunks is defined as an unsigned short, the max value is
65536. Assume the transfer_size reported by device is 4096, the
maximum size of DFU firmware supported is 65536 * 4096 = 256MB.

To support larger DFU firmware, we can change the guint16 to
guint32.

hughsie/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd,fwupd/fwupd,fwupd/fwupd