CHECK fails with ptp plugin and non default routes

[champtar]

I'm trying to switch from containerd to cri-o, and one big difference seems to be that cri-o call CheckNetworkList() https://github.com/cri-o/ocicni/blob/4fcbe80ee01fbc4c0401ae96537b3ee807c92c2c/pkg/ocicni/ocicni.go#L731

Here an example config that fails with Error checking network: Expected Route {Dst:{IP:198.18.128.0 Mask:ffff8000} GW:<nil>} not found in routing table

{
  "cniVersion": "0.4.0",
  "name": "mgmt",
  "type": "ptp",
  "ipMasq": true,
  "ipam": {
    "type": "host-local",
    "ranges": [
      [{"subnet": "198.18.0.0/17"}],
      [{"subnet": "fd61:7465:6d65:1000::/112"}]
    ],
    "routes": [
      { "dst": "0.0.0.0/0" },
      { "dst": "198.18.128.0/17" },
      { "dst": "198.19.254.254/32" },
      { "dst": "::/0" },
      { "dst": "fd61:7465:6d65:2000::/112" },
      { "dst": "fd61:7465:6d65:ffff::/128" }
    ]
  }
}

Using "cniVersion": "0.3.1" to bypass the check, the routes are created but with a gateway

# ip r
default via 198.18.0.1 dev eth0 
198.18.0.0/17 via 198.18.0.1 dev eth0 src 198.18.66.190 
198.18.0.1 dev eth0 scope link src 198.18.66.190 
198.18.128.0/17 via 198.18.0.1 dev eth0 
198.19.254.254 via 198.18.0.1 dev eth0 

If I keep only the default routes (v4 & v6) it works, but I actually need the more precise routes as my full use case is with multus and being able to configure some extra interfaces with any routes (/1 included)
Looking at the code I fail to see why default routes are a special case:

plugins/pkg/ip/utils_linux.go

Line 82 in 9f1f9a5

func ValidateExpectedRoute(resultRoutes []*types.Route) error {

related review: #264 (comment)