[TEST] mptcp diag.sh curious skips

Hi!

Every now and then this happens:

https://netdev-ctrl.bots.linux.dev/logs/vmksft/mptcp-dbg/results/478242/10-diag-sh/stdout

note the skip and the leak.

Not a big deal if this is a false positive given the very low freq. 
But the leak made me pause.