I prepared an alternative approach in rt46012_michal.  It slightly
refactors the code in configure_rpz() so that it reads a bit more nicely
by avoiding a double #ifdef and a triple dnsrps_enabled check while
retaining identical code flow.  As a bonus, it surrounds conf_dnsrps*
with an #ifdef to prevent a compiler warning when building without
DNSRPS support.  If you like it, feel free to use it.  Otherwise, your
fix is good to go as well.