net: qualcomm: rmnet: Add UL packet prioritization

Packets that have the skb->priority field set will now have a QMAPv5
checksum offload header with the new Priority bit marked as 1.

QMAPv5 checksum offload can continue to be used as normal with this
feature, and any combination of priority and csum offload is supported.

Change-Id: I2ce2483ed5f8cb35385ed6bcd64c717d136346a3
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>