Thanks to the previous commit, the MPTCP subflows are now closed on both
directions even when only the MPTCP path-manager of one peer asks for
their closure.

In the two tests modified here -- "userspace pm add & remove address"
and "userspace pm create destroy subflow" -- one peer is controlled by
the userspace PM, and the other one by the in-kernel PM. When the
userspace PM sends a RM_ADDR notification, the in-kernel PM will
automatically react by closing all subflows using this address. Now,
thanks to the previous commit, the subflows are properly closed on both
directions, the userspace PM can then no longer closes the same
subflows if they are already closed. Before, it was OK to do that,
because the subflows were still half-opened, still OK to send a RM_ADDR.

In other words, thanks to the previous commit closing the subflows, an
error will be returned to the userspace if it tries to close a subflow
that has already been closed. So no need to run this command, which mean
that the linked counters will then not be incremented.

These tests are then no longer sending both a RM_ADDR, then closing the
linked subflow just after. The test with the userspace PM on the server
side is now removing one subflow linked to one address, then sending
a RM_ADDR for another address. The test with the userspace PM on the
client side is now only removing the subflow that was previously
created.

Fixes: 4369c198 ("selftests: mptcp: test userspace pm out of transfer")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240826-net-mptcp-close-extra-sf-fin-v1-2-905199fe1172@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>