selftests: mptcp: join: validate event numbers

commit 20ccc7c5 upstream.

This test extends "delete and re-add" and "delete re-add signal" to
validate the previous commit: the number of MPTCP events are checked to
make sure there are no duplicated or unexpected ones.

A new helper has been introduced to easily check these events. The
missing events have been added to the lib.

The 'Fixes' tag here below is the same as the one from the previous
commit: this patch here is not fixing anything wrong in the selftests,
but it validates the previous fix for an issue introduced by this commit
ID.

Fixes: b911c97c ("mptcp: add netlink event support")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
[ Conflicts in mptcp_join.sh and mptcp_lib.sh, due to commit
  38f027fc ("selftests: mptcp: dump userspace addrs list") -- linked
  to a new feature, not backportable to stable -- and commit
  23a0485d ("selftests: mptcp: declare event macros in mptcp_lib")
  -- depending on the previous one -- not in this version. The conflicts
  in mptcp_join.sh were in the context, because a new helper had to be
  added after others that are not in this version. The conflicts in
  mptcp_lib.sh were due to the fact the other MPTCP_LIB_EVENT_*
  constants were not present. They have all been added in this version
  to ease future backports if any.
  In this version, it was also needed to import reset_with_events and
  kill_events_pids from the newer version, and adapt chk_evt_nr to how
  the results are printed in this version, plus remove the LISTENER
  events checks because the linked feature is not available in this
  kernel version. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>