usb: gadget: Enable DPL composition over ether tranpsort

Introduce new transport (ether) in f_qdss. Bind with u_ether if
transport is ether. Since DPL is a single IN endpoint only, updating
u_ether to treat the in/out endpoints as optional. Also fix a small
memory leak in the qdss function driver.

CRs-Fixed: 997061
Change-Id: I604a7b3c688131ba10003d7a25712f56b58bc323
Signed-off-by: Azhar Shaikh <azhars@codeaurora.org>
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>