selftests/bpf: remove unused toggle in tc_tunnel

selftests/bpf: remove unused toggle in tc_tunnel

tc_tunnel test is based on a send_and_test_data function which takes a
subtest configuration, and a boolean indicating whether the connection
is supposed to fail or not. This boolean is systematically passed to
true, and is a remnant from the first (not integrated) attempts to
convert tc_tunnel to test_progs: those versions validated for
example that a connection properly fails when only one side of the
connection has tunneling enabled. This specific testing has not been
integrated because it involved large timeouts which increased quite a
lot the test duration, for little added value.

Remove the unused boolean from send_and_test_data to simplify the
generic part of subtests.

Signed-off-by: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
Acked-by: Paul Chaignon <paul.chaignon@gmail.com>
Link: https://lore.kernel.org/r/20260403-tc_tunnel_cleanup-v1-1-4f1bb113d3ab@bootlin.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>