I'll assume the info you posted is when DHCP adds default route. So the relevant bits are:
/ip address print
3 D 178.160.xx.yyy/30 178.160.xx.yyy vlan-wap-isp
/ip route print
1 DS 0.0.0.0/0 178.160.xx.yyy 10
7 ADC 178.160.xx.yyy/30 178.160.xx.yyy vlan-wap-isp 0
(somehow I doubt that in route line 7 both addresses are exactly the same, only the first one suffixed with /30 netmask, I'd guess the yyy in second address is larger than yyy in first address by 1 but that's just guessing).
So if you want manually handle the routes via vlan-wap-isp interface, you have to add exactly the same two routes: the route towards 178.160.xx.yyy/30 subnet with gateway set to VLAN interface (line numbered 7 from your route print)
and route towards everything (
dst-address=0.0.0.0/0 via gateway on 178.160.xx.yyy/30 subnet (line 1 from your route print).