ipvlan: Unmask upper DSCP bits in ipvlan_process_v4_outbound()

[ Upstream commit 939cd1ab ]

Unmask the upper DSCP bits when calling ip_route_output_flow() so that
in the future it could perform the FIB lookup according to the full DSCP
value.

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: 27843ce6 ("ipvlan: ensure network headers are in skb linear part")
Signed-off-by: Sasha Levin <sashal@kernel.org>