Changes

tests/smpp: fix building for debian 13 armv7l

In Debian 13 armv7l, time_t is "long long int" instead of "long unsigned
int" as seen on x86_64 and aarch64. Fix it by casting to "long long
int".

Change-Id: I3801fc7d0a85036f1f9346c54824eff5c126f363