To handle multiple radio units we will need to rework this code significantly.
Move this to a dedicated routine as a preparatory step. The code moves out of
enb.cfg because later it will be also used in UEsim to configure simulator
radio units as well.

No non-whitespace changes in rendered enb.cfg and gnb.cfg .

/cc @jhuge, @lu.xu, @tomo, @xavier_thompson, @Daetalus