net: qualcomm: rmnet: Add support for GSO

Real devices may support scatter gather(SG), so enable SG on rmnet
devices to use GSO. GSO reduces CPU cycles by 20% for a rate of
146Mpbs for a single stream TCP connection.

CRs-Fixed: 2156182
Change-Id: Iabd914723a119c99d512de4a690323615585532c
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>