fix admin info peer to point to first endpoint (#5996)

The current problem is that when you invoke

```
mc admin info myminio | head -1
●  localhost:9000
```

This output is incorrect as the expected output should be
```
mc admin info myminio | head -1
●  192.168.1.17:9000
```

cmd/admin-rpc-client.go

@@ -256,7 +256,9 @@ type adminPeers []adminPeer
 func makeAdminPeers(endpoints EndpointList) (adminPeerList adminPeers) {
 	thisPeer := globalMinioAddr
 	if globalMinioHost == "" {
-		thisPeer = net.JoinHostPort("localhost", globalMinioPort)
+		// When host is not explicitly provided simply
+		// use the first IPv4.
+		thisPeer = net.JoinHostPort(sortIPs(localIP4.ToSlice())[0], globalMinioPort)
 	}
 	adminPeerList = append(adminPeerList, adminPeer{
 		thisPeer,