ip_tunnel: Do not use mark in skb by default

ip_tunnel: Do not use mark in skb by default

This reverts commit 584ebbc2a569175a7486f021660f8251a5c8fee4.

skb->mark contains the mark the encapsulated traffic which
can result in incorrect routing decisions being made such
as routing loops if the route chosen is via tunnel itself.
The correct method should be to use tunnel->fwmark.

Signed-off-by: Thomas Winter <thomas.winter@alliedtelesis.co.nz>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>