Thank you John for answering/addressing my question. Tried an air cored inductor, and the S21 attenuation was increasing almost linearly with frequency 1-300 MHz. So, as you said the the ferrite core is the reason behind this flat loss response.
I guess this means that I can use this inductor around FT23-43 effectively as an RF choke near Vcc with a bypass cap to ground for this frequency range which was the reason behind this test.
