Description of problem:

When configuring two BGPpeers with interface (BGP Unnumbered) rather then peer IP the frr webhook fails the second bgppeer as a duplicate.

Version-Release number of selected component (if applicable):

How reproducible: Easily

Steps to Reproduce:
1. Deploy a metallb resource
2. Create a BGPPeer with interface rather then IP address. 
3. Create a second BGPPeer with a different interface.
Actual results:

Error from server (Forbidden): error when creating "bgppeerv4-180.yaml": admission webhook "bgppeersvalidationwebhook.metallb.io" denied the request: peer  already exists, FRR mode doesn't support duplicate BGPPeers

Expected results:

To be able to create multiple bgppeers with different interfaces

Additional info:

bgppeer1
apiVersion: metallb.io/v1beta2
kind: BGPPeer
metadata:
name: peer-64500-ipv4-179
namespace: metallb-system
spec:
password: bgp-test
holdTime: 90s
keepaliveTime: 30s
connectTime: 10s
myASN: 64500
peerASN: 64500
interface: ens3f0np0.179
 
bgppeer2
apiVersion: metallb.io/v1beta2
kind: BGPPeer
metadata:
name: peer-64500-ipv4-180
namespace: metallb-system
spec:
password: bgp-test
holdTime: 90s
keepaliveTime: 30s
connectTime: 10s
myASN: 64500
peerASN: 64500
interface: ens3f0np0.180