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

[ Upstream commit c34cfe72 ]

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 via the tunnel key 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>