drivers: rmnet_shs: Add GSO support for TCP skbs

Previously TCP load was estimated based on the packet size
so load estimation varied based on coalescing ratio and data
size instead of the more direct measure of how many packets
each coalesced packet is made from.

With introduction of gso stamping for TCP packet load will be
estimated directly from packets received before coalescing.

Change-Id: I1e7bb127e14151ffb55697d0a25eca817106083b
Acked-by: Raul Martinez <mraul@qti.qualcomm.com>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>