drivers: rmnet_perf: Update logic for nonlinear SKBs

This is a revert of commit c5ca6535 ("Revert "drivers: rmnet_perf:
Update logic for nonlinear SKBs"") to restore rmnet_perf functionality.
This contains the missing fix for non-TCP/UDP packets on the legacy
(deaggregation) patch.

Orignal commit message:
Perf now has to handle nonlinear SKBs arriving over a new path from the
core RmNet driver. No deaggregation will be performed. Instead, perf's
job is to perform GRO on packets that (possibly) have GSO information
already present in the SKB.

Change-Id: I16ef4e4d4356a31ae9a8717e9bae563b42e84790
Signed-off-by: Sean Tranchetti <stranche@codeaurora.org>