Netty error log can be seen when server closes the connection after sending a goaway

[dilanSachi]

Description:
Usually after a server sends a GO_AWAY, it can close the connection. In the current implementation, when the client receives a GO_AWAY, the channel is put into a stale list and a timer task is run to close the stale channels (connections). This is put there as a measure to close the channels when the server does not close the connection. But in a scenario where the server closes the connection, the timer task will also try to close the connection again. This needs to be avoided.

Related internal issue - https://github.com/wso2-enterprise/internal-support-ballerina/issues/588