USB: gadget: f_mtp: Update header length correctly in send_file_work

Whenever data is transmitted from device to Host PC, MTP daemon sitting
in userspace writes to mtp driver through ioctl, which eventually
calls send_file_work to send data. Currently header length is not updated
properly to reflect correct length in case data file size is greater
than 4GB. Due to this, Host PC throws error when file of size > 4GB is
copied from device to Host PC. Hence fix the issue by updating header
length to (2 ^ 32 - 1) if length is greater than 4GB.

CRs-Fixed: 953737
Change-Id: I3840afb63f365c28bf3638b13b728800bc2419f4
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>