In the next patch we will switch usage of C Preprocessor to Jinja2, and in jinja2 doing set from under if, as e.g. in

    {%- if ru == 'm2ru' %}
    {%-   set n_antenna_ul = 1  %}
    {%- endif %}

does _not_ have the effect of setting n_antenna_ul=1 outside of the if block.

That, however, can be worked around with usage of namespace objects, so the following works as intended:

    {%- set x = namespace() %}
    {%- if ru == 'm2ru' %}
    {%-   set x.n_antenna_ul = 1  %}
    {%- endif %}

with x.n_antenna_ul=1 if ru was m2ru.

So taking into account this, and that in MultiRU ru will be denoting
RadioUnit-related configuration, let's switch ru to be a namespace object with
ru.ru_type denoting type of attached radio unit.

This both goes as a preparatory step for MultiRU and also allows to switch from
CPP to Jinja2 in the next patch.

/cc @lu.xu, @tomo, @xavier_thompson, @Daetalus
/reviewed-by @jhuge
/reviewed-on !1520