OPC-UA: only support the encryption policy selected in config.

By default open62541 client accepts all supported policies, but in makes problem
when negociating with some servers while most clients seems to only support
one policy at a time.

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{

     2

    "ID": "wamptest", 

     3

    "active": true, 

     4

    "protocolOptions": {

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        "autoPingInterval": 60, 

     6

        "autoPingTimeout": 20

     7

    }, 

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    "realm": "Automation", 

     9

    "url": "ws://127.0.0.1:8888"

    10

}