usb: gadget: rndis: Add new rndis parameters

Add pkt_alignment_factor rndis parameter. This
parameter along with max_pkt_per_xfer allow rndis
function driver to aggregate more than one IP packets
per transfer. This is done by calling newly added API
rndis_set_pkt_alignment_factor().

Change-Id: Ic9c543c388f872452e708a3a26be4ae82b54c082
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>