Merge branch 'net-add-support-for-ip-generic-checksum-offload-for-gre'

Xin Long says:

====================
net: add support for ip generic checksum offload for gre

This patchset it to add ip generic csum processing first in
skb_csum_hwoffload_help() in Patch 1/2 and then add csum
offload support for GRE header in Patch 2/2.
====================

Link: https://lore.kernel.org/r/cover.1611825446.git.lucien.xin@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>