Don't repeat slapparameter_dict['ncell_list'][k] - we can introduce a name for
current neighbour cell, and use that name in the loop. And align entries to
that they read more clearly.

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

/cc @jhuge, @lu.xu, @tomo, @xavier_thompson, @Daetalus
/proposed-for-review-on nexedi/slapos!1526
/reviewed-by TrustMe