mptcp: fix address removal logic in mptcp_pm_nl_rm_addr

JIRA: https://issues.redhat.com/browse/RHEL-115576
Upstream Status: net-next.git commit 92e239e
Conflicts:
  net/mptcp/pm_kernel.c: context mismatch because of missing backport of
  upstream commit 37712d8 ("mptcp: pm: in-kernel: rename 'add_addr_accept_max' to
 'limit_add_addr_accepted'")

commit 92e239e
Author: Gang Yan <yangang@kylinos.cn>
Date:   Tue Nov 18 08:20:28 2025 +0100

    mptcp: fix address removal logic in mptcp_pm_nl_rm_addr

    Fix inverted WARN_ON_ONCE condition that prevented normal address
    removal counter updates. The current code only executes decrement
    logic when the counter is already 0 (abnormal state), while
    normal removals (counter > 0) are ignored.

    Signed-off-by: Gang Yan <yangang@kylinos.cn>
    Fixes: 6361139 ("mptcp: pm: remove '_nl' from mptcp_pm_nl_rm_addr_received")
    Cc: stable@vger.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-v1-10-806d3781c95f@kernel.org
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Davide Caratti <dcaratti@redhat.com>

Author: dcaratti

net/mptcp/pm_kernel.c

@@ -542,7 +542,7 @@ static void mptcp_pm_nl_add_addr_received(struct mptcp_sock *msk)
 
 void mptcp_pm_nl_rm_addr(struct mptcp_sock *msk, u8 rm_id)
 {
-	if (rm_id && WARN_ON_ONCE(msk->pm.add_addr_accepted == 0)) {
+	if (rm_id && !WARN_ON_ONCE(msk->pm.add_addr_accepted == 0)) {
 		/* Note: if the subflow has been closed before, this
 		 * add_addr_accepted counter will not be decremented.
 		 */