Fix connection timeout configuration for Netty

[bclozel]

As of #15385, Spring Boot can configure the server connection timeout for Netty servers.
We're using the server.connection-timeout configuration property for that and applying it directly to Netty as a channel option.

In #15368 (comment), it seems that -1 and 0 values don't mean the same thing for Netty:

• -1 is an illegal value, we should map it to 0 instead as this is the value that disables the connection timeout for Netty
• 0 is not the default value for Netty and it disables the connection timeout. We should instead ignore completely this value and not set anything for Netty

See the Netty ChannelConfig.

[philwebb]

Closed in favor of PR #16535

[izeye]

Based on @philwebb‘s comment, this seems meant to be closed.