Function otPlatDnsIsUpstreamQueryAvailable 

pub unsafe extern "C" fn otPlatDnsIsUpstreamQueryAvailable(
    aInstance: *mut otInstance,
) -> bool

Indicates whether upstream DNS query functionality is available on the platform.

This function allows the platform to inform the OpenThread stack if no upstream DNS server is available.

This function is used to optimize query handling. If this function returns false (e.g., no upstream DNS server is currently available), one can avoid attempting an upstream resolution (which would likely time out) and instead immediately send an appropriate negative response (e.g., SERVFAIL) to the DNS client.

@param[in] aInstance The OpenThread instance.

@retval TRUE Upstream DNS query functionality is available. @retval FALSE Upstream DNS query functionality is not available.