net: rmnet_usb: Add support for aligned QOS header

When QOS is enabled, QOS header of 6 bytes appended to
the network packet.This is making the network packet buffer unaligned.
USB hardware has some penalty with dealing the unaligned buffers Due to
this Bi-Direction throughput is dropped.

Introduce a new QOS header of size 8 bytes. Add a new ioctl to know
which QOS header need to be used.

CRs-Fixed: 583165
Change-Id: I11bb56d2dbbc1262345e091241dcf6f681643e84
Signed-off-by: ChandanaKishori Chiluveru <cchilu@codeaurora.org>