staticd: Extend `ip_route_vrf` CLI to support SRv6 traffic steering

staticd: Extend `ip_route_vrf` CLI to support SRv6 traffic steering

staticd already has a CLI to steer IPv6 traffic over a given SRv6 SID
list:

```
vrf vrf10
 ipv6 route 2001:db8:1:1::/64 sr0 segments fcbb:bbbb:1:2:3:fe00::
```

This PR extends the existing CLI `ip route` to support steering of IPv4
traffic over an SRv6 SID list.

```
vrf vrf10
 ip route 10.0.0.0/24 sr0 segments fcbb:bbbb:1:2:3:fe00::
```

Signed-off-by: Carmine Scarpitta <cscarpit@cisco.com>