mptcp: pm: fix RM_ADDR ID for the initial subflow

[ Upstream commit 87b5896f3f7848130095656739b05881904e2697 ]

The initial subflow has a special local ID: 0. When an endpoint is being
deleted, it is then important to check if its address is not linked to
the initial subflow to send the right ID.

If there was an endpoint linked to the initial subflow, msk's
mpc_endpoint_id field will be set. We can then use this info when an
endpoint is being removed to see if it is linked to the initial subflow.

So now, the correct IDs are passed to mptcp_pm_nl_rm_addr_or_subflow(),
it is no longer needed to use mptcp_local_id_match().

Fixes: 3ad14f54

 ("mptcp: more accurate MPC endpoint tracking")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>