usb: gadget: u_bam: Make OUT(or RX) request buffer size 1KB aligned

Synopsys USB3 Controller (DWC3) has a restriction where size
of OUT requests (TRB) queued to the controller must be aligned
with the endpoint's max packet size. Hence, change u_bam (RMNET
transport) driver to submit OUT request of size 2KB.

Change-Id: I60b77676827155f1674c676fb454bbb831388683
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>