Revert "mptcp: add needs_id for netlink appending addr"

Revert "mptcp: add needs_id for netlink appending addr"

[ Upstream commit 8e2760eaab778494fc1fa257031e0e1799647f46 ]

This commit was originally adding the ability to add MPTCP endpoints
with ID 0 by accident. The in-kernel PM, handling MPTCP endpoints at the
net namespace level, is not supposed to handle endpoints with such ID,
because this ID 0 is reserved to the initial subflow, as mentioned in
the MPTCPv1 protocol [1], a per-connection setting.

Note that 'ip mptcp endpoint add id 0' stops early with an error, but
other tools might still request the in-kernel PM to create MPTCP
endpoints with this restricted ID 0.

In other words, it was wrong to call the mptcp_pm_has_addr_attr_id
helper to check whether the address ID attribute is set: if it was set
to 0, a new MPTCP endpoint would be created with ID 0, which is not
expected, and might cause various issues later.

Fixes: 584f38942626 ("mptcp: add needs_id for netlink appending addr")
Cc: stable@vger.kernel.org
Link: https://datatracker.ietf.org/doc/html/rfc8684#section-3.2-9
Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260407-net-mptcp-revert-pm-needs-id-v2-1-7a25cbc324f8@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ applied changes to net/mptcp/pm_netlink.c instead of renamed net/mptcp/pm_kernel.c ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>