[ upstream commit 853fec659702b724295b83e0df8b282c033933f6 ]

As lbmap.DumpServiceMapsToUserspace returns a list of backend services,
this list of backend services can contain duplicated entries as BPF lb
map can contain multiple entries for the same service as showned from the
following log messages:

```
level=debug msg="parsing service mapping" bpfMapKey="10.98.234.114:9125" bpfMapValue="0.0.0.0:0 (0)" subsys=map-lb
level=debug msg="converting ServiceKey and ServiceValue to frontend and backend" obj="0.0.0.0:0 (0)" serviceID="10.98.234.114:9125" subsys=map-lb
level=debug msg="creating L3n4Addr for ServiceKey" serviceID="10.98.234.114:9125" subsys=map-lb
level=debug msg="adding frontend and backend to SVCMap" backend="0.0.0.0:0, weight: 0" backendIndex=0 frontend="10.98.234.114:9125" subsys=loadbalancer
level=debug msg="parsing service mapping" bpfMapKey="10.98.234.114:9125" bpfMapValue="10.10.1.222:9125 (29)" subsys=map-lb
level=debug msg="converting ServiceKey and ServiceValue to frontend and backend" obj="10.10.1.222:9125 (29)" serviceID="10.98.234.114:9125" subsys=map-lb
```

In order to correctly remove this list of services that are no longer
being managed by k8s one should use a Set to avoid trying to delete
multiple times the same LB service which results in controller errors
such as:

```
msg="Controller run failed" consecutiveErrors=2 error="Errors deleting BPF map entries: key 10.98.234.114:42275 is not in lbmap...
```

Fixes: cc4be8e37107 ("daemon: sync BPF maps with in-memory K8s service maps")
Signed-off-by: André Martins <andre@cilium.io>
Signed-off-by: Joe Stringer <joe@cilium.io>