Support subnet host-routes by adding InterfaceRouteTable to the ports

Do you mean also add the subnet_id ?

you want something like below
intf_rt_name = 'NEUTRON_IFACE_RT_'  + str(subnet_id) + " : " + str(port_obj.uuid) 

You prefer subnet_id or subnet_cidr ?
eg. intf_rt_name = 'NEUTRON_IFACE_RT_'  + str(subnet_cidr) + " : " + str(port_obj.uuid)

Note that, presently atleast the plugin doesn't support to create a port having two ip addresses belonging to two subnets.