Bluetooth-OPP: Enable support to send multiple files

Change will add support to send multiple files. Otherwise, if
same file is selected to send multiple times after first transfer
succeeds queued instances of the same file got removed and its shown
as failed to sent.

CRs-Fixed: 561121
Change-Id: Ifcaee3f8a6373773d0bccfc36899f81f8fd73f26