connections.total-connections count can get negative

[mikkokar]

The problem

Styx connections.total-connections count can get negative.

Detailed description

Most likely culprit is the channelRegistered handler in ExcessConnectionRejector.

@Override
public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
    if (channelGroup.size() >= maxConnectionsCount) {
        LOGGER.warn("Max allowed connection  to server exceeded: current={} configured={}", channelGroup.size(), maxConnectionsCount);
        ctx.close();
        return;
    }
    channelGroup.add(ctx.channel());
    super.channelRegistered(ctx);
}

I suspect calling ctx.close() fromchannelRegistered triggers a channelInactive event without corresponding channelActive. As a result, ChannelStatisticsHandler ends up seeing more channel inactive than channel active events, and the count may drift below zero.

Acceptance criteria

• A rejected connection is neutral with respect to total-connections count.

[mikkokar]

Fyi @taer ^^^.

[kvosper]

Merged #360