pkts from rmnet device are sent as SG, we see poor
throughput when transmitting these SG frames using
an MSDU extension descriptor. to resolve this issue
we identify if the frame is from RMNET device and if so
copy the headers from skb linear address to the frag
address and provide the frag address to HW for transmission
CRs-Fixed: 3337822
Change-Id: Ic1b7d9f861dcd4f838509772c45e47d3917fc59f