selftests: mptcp: connect: fix comment typo

Spell "transmissions" properly.

Found by searching for keyword "tranm".

Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Yueh-Shun Li <shamrocklee@posteo.net>
Signed-off-by: Mat Martineau <martineau@kernel.org>
Link: https://lore.kernel.org/r/20230623-send-net-next-20230623-v1-8-a883213c8ba9@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>