What on earth are you trying to do?

It should be Fiber -> TM Provided Modem -> Fortigate -> Switches -> D-Link

all the router work should already be done on the Fortigate
the D-Link isnt the one handling the network in this case

so why on earth do you need to bridge it?

Do you need more lan ports? get a switch
Do you need wifi coverage? AP Mode

I fail to see why do you need this d-link at all on the network