selftests: forwarding: vxlan_bridge_1d: use more proper tos value

[ Upstream commit 9b64208f ]

0x11 and 0x12 set the ECN bits based on RFC2474, it would be better to avoid
that. 0x14 and 0x18 would be better and works as well.

Reported-by: Petr Machata <petrm@mellanox.com>
Fixes: 4e867c9a ("selftests: forwarding: vxlan_bridge_1d: fix tos value")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>