net: qualcomm: rmnet: Avoid unnecessary RSB/RSC SKB allocation

If the coalescing frame we receive does not need to be segmented because
of checksum errors or varying packet lengths, we can pass off the original
SKB instead of allocating a new one that holds all the same data.

Change-Id: Id1a41c69daec8c99f75ffeeb3e179534c80b9076
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>