Netstack does not add src IP in created network rules

I am trying to use gVisor as a runtime along with the gvisor-containerd-shim in Kubernetes. The Kubernetes pods are able to talk to each other using their internal IPs but it seems that the created IP rules lack the src IP field causing replies from an internet host to not reach the pod. I am using the WeaveNet plugin for networking.

Running `kubectl exec dnsutils ip route show all` on the [dnsutils](https://k8s.io/examples/admin/dns/dnsutils.yaml) pod with the default containerd runtime gives this output:
```
default via 10.44.0.0 dev eth0
10.32.0.0/12 dev eth0 src 10.44.0.1
```
whereas using gVisor it gives:
```
127.0.0.0/8 dev lo
::1 dev lo
10.32.0.0/12 dev eth0
fe80::/64 dev eth0
default via 10.44.0.0 dev eth0
```