Dual stack cluster fails on installation when multi-path routing entries exist

We observed that a dual stack cluster deployed with AI gui only fails.
This cluster is dhcp for ipv4, RA/RS autoconfiguration for ipv6.

It fails with error in the onvkube container

```
I0906 07:45:43.044090   87450 gateway_init.go:261] Initializing Gateway Functionality
I0906 07:45:43.046398   87450 gateway_localnet.go:152] Node local addresses initialized to: map[10.131.31.214:{10.131.31.208 fffffff0} 10.255.0.2:{10.255.0.0 fffffe00} 127.0.0.1:{127.0.0.0 ff000000} 2001:1b74:480:613a:f6e9:d4ff:fef1:6f26:{2001:1b74:480:613a:: ffffffffffffffff0000000000000000} ::1:{::1 ffffffffffffffffffffffffffffffff} fd01:0:0:1::2:{fd01:0:0:1:: ffffffffffffffff0000000000000000} fe80::8ce9:b4ff:fe1a:1208:{fe80:: ffffffffffffffff0000000000000000} fe80::c8ef:ecff:fee3:64c7:{fe80:: ffffffffffffffff0000000000000000} fe80::f6e9:d4ff:fef1:6f26:{fe80:: ffffffffffffffff0000000000000000}]
I0906 07:45:43.047759   87450 helper_linux.go:71] Provided gateway interface "br-ex", found as index: 7
I0906 07:45:43.048045   87450 helper_linux.go:97] Found default gateway interface br-ex 10.131.31.209
I0906 07:45:43.048152   87450 helper_linux.go:71] Provided gateway interface "br-ex", found as index: 7
F0906 07:45:43.048318   87450 ovnkube.go:133] failed to get default gateway interface
```

on the node we observed that there is multi-path entry during

```
default proto ra metric 48 pref medium
        nexthop via fe80::e2f6:2d01:ab14:ec71 dev br-ex weight 1
        nexthop via fe80::e2f6:2d01:ab11:c271 dev br-ex weight 1
```

I manually remove one of the entries (`ip route delete`) and then delete the ovnkube-node pod. Then the installation continues, container works.

Every time there is multiple entry, if the onvkube-node starts, it fails.

4.10.30

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There might a side issue: the interface of the node upon boot takes time to get the ipv6 autoconfiguration, no RS packets seemed to be sent out (observed zero on all routers).