selftests: mptcp: decrease BW in simult flows

When running the simult_flow selftest in slow environments -- e.g. QEmu without KVM support --, the results can be unstable. This selftest checks if the aggregated bandwidth is (almost) fully used as expected.

To help improving the stability while still keeping the same validation in place, the BW and the delay are reduced to lower the pressure on the CPU.

---
Notes:
- Conflicts in simult_flows.sh, because v5.15 doesn't have commit 675d99338e7a ("selftests: mptcp: simult flows: format subtests results in TAP") which modifies the context for a new but unrelated feature.
- This is a new version to the one recently proposed by Sasha, this time without dependences:
https://lore.kernel.org/stable/[email protected]/
- This is the same patch as the one recently sent for v6.1:
https://lore.kernel.org/stable/[email protected]/

---
 tools/testing/selftests/net/mptcp/simult_flows.sh | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

index 752cef168804..cab3e3a5481d 100755
@@ -289,10 +289,11 @@ done
 
 setup
 run_test 10 10 0 0 "balanced bwidth"
-run_test 10 10 1 50 "balanced bwidth with unbalanced delay"
+run_test 10 10 1 25 "balanced bwidth with unbalanced delay"
 
 # we still need some additional infrastructure to pass the following test-cases
-run_test 30 10 0 0 "unbalanced bwidth"
-run_test 30 10 1 50 "unbalanced bwidth with unbalanced delay"
-run_test 30 10 50 1 "unbalanced bwidth with opposed, unbalanced delay"
+run_test 10 3 0 0 "unbalanced bwidth"
+run_test 10 3 1 25 "unbalanced bwidth with unbalanced delay"
+run_test 10 3 25 1 "unbalanced bwidth with opposed, unbalanced delay"
+
 exit $ret

2.43.0