selftests: forwarding: vxlan_bridge_1d: fix tos value

After commit 71130f29 ("vxlan: fix tos value before xmit") we start
strict vxlan xmit tos value by RT_TOS(), which limits the tos value less
than 0x1E. With current value 0x40 the test will failed with "v1: Expected
to capture 10 packets, got 0". So let's choose a smaller tos value for
testing.

Fixes: d417ecf5 ("selftests: forwarding: vxlan_bridge_1d: Add a TOS test")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>