SNTP implementation defined symbols like "MODE_MASK", which can easily
conflict with similary laxly defined symbols in other modules, and
indeed, we hit a case like that (below). So, prefix these symbols
consistently with "SNTP_", until more clear private namespacing
convention are made pervasive in Zephyr.
subsys/net/lib/sntp/sntp_pkt.h:14: error: "MODE_MASK" redefined
include/arch/arm/aarch32/cortex_a_r/cpu.h:17: note: this is the
location of the previous definition
Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>