xds nonce is reused between xds streams

[kyessenov]

Using SotW xDS:

[client 19:55:28.305][296173][debug][router] [external/envoy/source/common/router/router.cc:520] [Tags: "ConnectionId":"0","StreamId":"5851133085805278286"] cluster 'xds_cluster' match for URL '/envoy.service.discovery.v3.AggregatedDiscoveryService/StreamAggregatedResources'
[client 19:55:28.306][296173][debug][router] [external/envoy/source/common/router/router.cc:732] [Tags: "ConnectionId":"0","StreamId":"5851133085805278286"] router decoding headers:
':method', 'POST'
':path', '/envoy.service.discovery.v3.AggregatedDiscoveryService/StreamAggregatedResources'
':authority', 'xds_cluster'
':scheme', 'http'
'te', 'trailers'
'content-type', 'application/grpc'
'x-envoy-internal', 'true'
'x-forwarded-for', '192.168.97.199'

[client 19:55:28.306][296173][debug][pool] [external/envoy/source/common/conn_pool/conn_pool_base.cc:265] [Tags: "ConnectionId":"0"] using existing fully connected connection
[client 19:55:28.306][296173][debug][pool] [external/envoy/source/common/conn_pool/conn_pool_base.cc:182] [Tags: "ConnectionId":"0"] creating stream
[client 19:55:28.306][296173][debug][router] [external/envoy/source/common/router/upstream_request.cc:563] [Tags: "ConnectionId":"0","StreamId":"5851133085805278286"] pool ready
[client 19:55:28.306][296173][trace][pool] [external/envoy/source/common/conn_pool/conn_pool_base.cc:131] not creating a new connection, shouldCreateNewConnection returned false.
[client 19:55:28.306][296173][trace][router] [external/envoy/source/common/router/upstream_codec_filter.cc:61] [Tags: "ConnectionId":"0","StreamId":"5851133085805278286"] proxying headers
[client 19:55:28.306][296173][trace][http2] [external/envoy/source/common/http/http2/codec_impl.cc:1315] [Tags: "ConnectionId":"0"] about to send frame type=1, flags=4
[client 19:55:28.306][296173][trace][http2] [external/envoy/source/common/http/http2/codec_impl.cc:1337] [Tags: "ConnectionId":"0"] send data: bytes=75
[client 19:55:28.306][296173][trace][connection] [external/envoy/source/common/network/connection_impl.cc:529] [Tags: "ConnectionId":"0"] writing 75 bytes, end_stream false
[client 19:55:28.306][296173][trace][http2] [external/envoy/source/common/http/http2/codec_impl.cc:1208] [Tags: "ConnectionId":"0"] sent frame type=1, stream_id=3, length=66
[client 19:55:28.306][296173][trace][http] [external/envoy/source/common/http/filter_manager.cc:572] [Tags: "ConnectionId":"0","StreamId":"5851133085805278286"] decode headers called: filter=envoy.filters.http.upstream_codec status=0
[client 19:55:28.310][296173][trace][config] [external/envoy/source/extensions/config_subscription/grpc/grpc_mux_impl.cc:123] Sending DiscoveryRequest for type.googleapis.com/envoy.config.cluster.v3.Cluster: version_info: "0"  type_url: "type.googleapis.com/envoy.config.cluster.v3.Cluster" response_nonce: "1"
[client 19:55:28.311][296173][trace][router] [external/envoy/source/common/router/upstream_codec_filter.cc:93] [Tags: "ConnectionId":"0","StreamId":"5851133085805278286"] proxying 34156 bytes```

As you can see on re-connect, response_nonce is set to "1" which is from the previous xDS stream. This is a violation of xDS which states that nonce does not survive stream restarts.

CC @adisuissa

[kyessenov]

Probably related to #15767