default or selected kernelversion does not have config value CONFIG_NET_ESTIMATOR.
Result is shown for kernelversion 5.4.123

Rate estimator


Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>QoS and/or fair queueing
└─>Rate estimator
In linux kernel since version 2.6.12  
In order for Quality of Service scheduling to work, the current
rate-of-flow for a network device has to be estimated; if you say Y
here, the kernel will do just that.