[golang/go] net: improve documentation for net.Dialer.FallbackDelay

### ROOT CAUSE The issue highlights that the documentation for `net.Dialer.FallbackDelay` is insufficient. The field's purpose and behavior are not clearly explained, particularly regarding how it affects the timing of retries when multiple addresses are provided. The current documentation does not explicitly state that `FallbackDelay` controls the delay between attempts to connect to subsequent addresses, leading to potential misuse or misunderstanding. ### CODE FIX Update the documentation for `net.Dialer.FallbackDelay` to clarify its behavior and provide examples. The fix involves modifying the comment in the `Dialer` struct to include a detailed explanation and example. ```go // FallbackDelay is the delay before trying the next address in a list // of addresses returned by a name resolver. It is zero, meaning no // delay. The Dialer will use this delay when the first address in the // list fails, then the second, and so on. // // For example, if FallbackDelay is 100ms and the resolver returns three // addresses, the Dialer will try the first address immediately, then if // that fails, wait 100ms before trying the second, and then wait another // 100ms before trying the third. FallbackDelay time.Duration ``` This change ensures developers understand that `FallbackDelay` applies to subsequent retries and not just the initial delay, and provides a concrete example of how the delay accumulates between attempts.