ddsi_time_t.seconds should be uint32_t

[binbowang1987]

ref DDSI-RTPS 9.3.2.1 IDL Definitions

struct Time_t {
  unsigned long seconds; // time in seconds
  unsigned long fraction; // time in sec/2^32
};

[binbowang1987]

@eboasson
when encounter this timestamp, it will be overflowed and cause cxx version to throw exception.

void dds::core::Time::sec(int64_t s)
{
    if(s < 0 && s != -1) {
        ISOCPP_THROW_EXCEPTION(ISOCPP_ERROR, "dds::core::Time::sec out of bounds");
    } else {
        /** @internal @bug OSPL-2308 RTF Time-ish coercion issue
        @see http://jira.prismtech.com:8080/browse/OSPL-2308 */
        sec_ =  s;
    }
}