selftests: mptcp: add missing join check

selftests: mptcp: add missing join check

commit 857898eb4b28daf3faca3ae334c78b2bb141475e upstream.

This function also writes the name of the test with its ID, making clear
a new test has been executed.

Without that, the ADD_ADDR results from this test was appended at the
end of the previous test causing confusions. Especially when the second
test was failing, we had:

  17 signal invalid addresses     syn[ ok ] - synack[ ok ] - ack[ ok ]
                                  add[ ok ] - echo  [ ok ]
                                  add[fail] got 2 ADD_ADDR[s] expected 3

In fact, this 17th test was OK but not the 18th one.

Now we have:

  17 signal invalid addresses     syn[ ok ] - synack[ ok ] - ack[ ok ]
                                  add[ ok ] - echo  [ ok ]
  18 signal addresses race test   syn[fail] got 2 JOIN[s] syn expected 3
   - synack[fail] got 2 JOIN[s] synack expected
   - ack[fail] got 2 JOIN[s] ack expected 3
                                  add[fail] got 2 ADD_ADDR[s] expected 3

Fixes: 33c563ad28e3 ("selftests: mptcp: add_addr and echo race test")
Reported-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Conflict in mptcp_join.sh, because commit 86e39e04482b ("mptcp: keep
  track of local endpoint still available for each msk") is not in this
  version and changed the context. The same line can still be applied at
  the same place. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>