l2tp: Add support for zero IPv6 checksums

Added new L2TP configuration options to allow TX and RX of
zero checksums in IPv6. Default is not to use them.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc include/uapi/linux/l2tp.h
Simple merge

diff --cc net/l2tp/l2tp_core.c
Simple merge

diff --cc net/l2tp/l2tp_core.h
Simple merge

diff --cc net/l2tp/l2tp_netlink.c
Simple merge