ipv4: ip_tunnel: Unmask upper DSCP bits in ip_tunnel_xmit()

[ Upstream commit c2b639f9 ]

Unmask the upper DSCP bits when initializing an IPv4 flow key via
ip_tunnel_init_flow() before passing it to ip_route_output_key() so that
in the future we could perform the FIB lookup according to the full DSCP
value.

Note that the 'tos' variable includes the full DS field. Either the one
specified as part of the tunnel parameters or the one inherited from the
inner packet.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: b5a7b661 ("net: Fix netns for ip_tunnel_init_flow()")
Signed-off-by: Sasha Levin <sashal@kernel.org>