Merge branch 'selftests-mptcp-join-pass-args-in-new-env-vars'

Matthieu Baerts says:

====================
selftests: mptcp: join: pass args in new env vars

In this series, Geliang did some refactoring in the mptcp_join.sh file.

Patch 1 reduces the scope of some global env vars, only used by some
tests: easier to deal with.

Patch 2 uses a dedicated env var for fastclose case instead of re-using
addr_nr_ns2 with embedded info, clearer.

Patch 3 is similar but for the fullmesh case.

Patch 4 moves a positional but optional argument of run_tests() to an
env var like it has already been done with the other args, cleaner.
====================

Link: https://lore.kernel.org/r/20230712-upstream-net-next-20230712-selftests-mptcp-use-local-env-v1-0-f1c8b62fbf95@tessares.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>