mptcp: pm: kernel: reset fullmesh counter after flush

commit 1774d3c upstream.

This variable counts how many MPTCP endpoints have a 'fullmesh' flag
set. After having flushed all MPTCP endpoints, it is then needed to
reset this counter.

Without this reset, this counter exposed to the userspace is wrong, but
also non-fullmesh endpoints added after the flush will not be taken into
account to create subflows in reaction to ADD_ADDRs.

Fixes: f88191c ("mptcp: pm: in-kernel: record fullmesh endp nb")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260422-mptcp-inc-limits-v6-0-903181771530%40kernel.org?part=15
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260427-net-mptcp-misc-fixes-7-1-rc2-v1-4-7432b7f279fa@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: matttbe

net/mptcp/pm_kernel.c

@@ -1278,6 +1278,7 @@ static void __reset_counters(struct pm_nl_pernet *pernet)
 	WRITE_ONCE(pernet->endp_signal_max, 0);
 	WRITE_ONCE(pernet->endp_subflow_max, 0);
 	WRITE_ONCE(pernet->endp_laminar_max, 0);
+	WRITE_ONCE(pernet->endp_fullmesh_max, 0);
 	pernet->endpoints = 0;
 }