core: rpc - replaced api member printf with rpl_printf

- clang is throwing error: no member named '__printf_chk' in 'struct rpc'
- reported in FS#457, follwing report on Debian:
  https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=755852
core: dns_cache rpc commands updated to use rpl_printf()
core: dst_blacklist rpc commands updated to use rpl_printf()
app_lua: rpc commands updated to use rpl_printf()
cfg_rpc: rpc commands updated to use rpl_printf()
ctl: rpc commands updated to use rpl_printf()
db_text: rpc commands updated to use rpl_printf()
dialog: rpc commands updated to use rpl_printf()
drouting: rpc commands updated to use rpl_printf()
jsonrpc-s: rpc commands updated to use rpl_printf()
kex: rpc commands updated to use rpl_printf()
mi_rpc: rpc commands updated to use rpl_printf()
pipelimit: rpc commands updated to use rpl_printf()
permissions: rpc commands updated to use rpl_printf()
prefix_route: rpc commands updated to use rpl_printf()
presence: rpc commands updated to use rpl_printf()
pv: rpc commands updated to use rpl_printf()
qos: rpc commands updated to use rpl_printf()
ratelimit: rpc commands updated to use rpl_printf()
sca: rpc commands updated to use rpl_printf()