Don't create static subnet routes for subnets with different IP protocol

[BenjaminLudwigSAP]

In Neutron different subnets of the same network can have different IP versions (IPv4/IPv6).
If two subnets of the same network have different IP versions, no load balancers can be created or updated. Because as soon as the static subnet routes are created, VLAN creation fails because if there is a route into an IPv6 subnet, there must be an IPv6 SelfIP too.

Steps to reproduce

1. Create an Openstack network with an IPv4 subnet and an IPv6 subnet.
2. Create a load balancer in one of the subnets.

Expected behavior

• The load balancer is successfully created.
• There is a static subnet route for the other subnet, even though it has a different IP version.

Observed behavior

• The load balancer is stuck in PENDING_CREATE.
• There is no static subnet route for the other subnet, since it has a different IP version.

Solution

There are two possible solutions:

• Create an IPv6 SelfIP if a static IPv6 route was created.
• Don't create static IPv6 routes. This is the easier and thus the for now preferred solution.

Notes

• Since it's possible that this bug only surfaces at rescheduling (e.g. when an IPv6 subnet is created without an LB in a network with another IPv4 subnet with LBs and then one of them is rescheduled), I have added the rescheduling label as well.