selftests: mptcp: add explicit test case for remove/readd

From: Paolo Abeni <pabeni@redhat.com>

commit b5e2fb832f48bc01d937a053e0550a1465a2f05d upstream.

Delete and re-create a signal endpoint and ensure that the PM
actually deletes and re-create the subflow.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: e06959e9eebd ("selftests: mptcp: join: test for flush/re-add endpoints")
[ No conflicts, but adapt the test to the helpers in this version:
  - run_tests has been modified a few times to reduce the number of
    positional parameters
  - no pm_nl_check_endpoint helper
  - no chk_mptcp_info helper
  - chk_subflow_nr taking an extra parameter
  - kill_tests_wait instead of mptcp_lib_kill_wait ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>