Revert "net: ip_tunnel: make sure to pull inner header in ip_tunnel_rcv()"

This reverts commit 5c033870 which is
commit b0ec2abf upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Ia0eb476c521977b863898ceeeaa664daf08bdb88
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>