mptcp: pm: check add_addr_accept_max before accepting new ADD_ADDR

commit 0137a3c7 upstream.

The limits might have changed in between, it is best to check them
before accepting new ADD_ADDR.

Fixes: d0876b22 ("mptcp: add the incoming RM_ADDR support")
Cc: stable@vger.kernel.org
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20240819-net-mptcp-pm-reusing-id-v1-10-38035d40de5b@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Conflicts in pm_netlink.c, because the context is different, but the
  same lines can still be modified to fix the issue. This is due to
  commit 322ea377 ("mptcp: pm: only mark 'subflow' endp as
  available") not being backported to this version. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>