selftests: mptcp: call test_fail without argument

This patch modifies test_fail() to call mptcp_lib_pr_fail() only if there
are arguments (if [ ${#} -gt 0 ]) in userspace_pm.sh, add arguments
"unexpected type: ${type}" when calling test_fail() from test_remove().
Then mptcp_lib_pr_fail() can be used in check_expected_one() instead of
test_fail().

The same in mptcp_join.sh, calling fail_test() without argument, and adapt
this helper not to call print_fail() in this case.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://lore.kernel.org/r/20240308-upstream-net-next-20240308-selftests-mptcp-unification-v1-10-4f42c347b653@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>