mptcp: decouple mptcp fastclose from tcp close

mptcp: decouple mptcp fastclose from tcp close

commit fff0c87996672816a84c3386797a5e69751c5888 upstream.

With the current fastclose implementation, the mptcp_do_fastclose()
helper is in charge of two distinct actions: send the fastclose reset
and cleanup the subflows.

Formally decouple the two steps, ensuring that mptcp explicitly closes
all the subflows after the mentioned helper.

This will make the upcoming fix simpler, and allows dropping the 2nd
argument from mptcp_destroy_common(). The Fixes tag is then the same as
in the next commit to help with the backports.

Fixes: d21f83485518 ("mptcp: use fastclose on more edge scenarios")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Geliang Tang <geliang@kernel.org>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20251118-net-mptcp-misc-fixes-6-18-rc6-v1-5-806d3781c95f@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>