AP_GPS: fixed GPS time in HIL

account for 10 year difference in epoch between unix time and GPS time

libraries/AP_GPS/AP_GPS.cpp

@@ -393,8 +393,9 @@ AP_GPS::setHIL(uint8_t instance, GPS_Status _status, uint64_t time_epoch_ms,
     istate.num_sats = _num_sats;
     istate.have_vertical_velocity = _have_vertical_velocity;
     istate.last_gps_time_ms = tnow;
-    istate.time_week     = time_epoch_ms / (86400*7*(uint64_t)1000);
-    istate.time_week_ms  = time_epoch_ms - istate.time_week*(86400*7*(uint64_t)1000);
+    uint64_t gps_time_ms = time_epoch_ms - (17000ULL*86400ULL + 52*10*7000ULL*86400ULL - 15000ULL);
+    istate.time_week     = gps_time_ms / (86400*7*(uint64_t)1000);
+    istate.time_week_ms  = gps_time_ms - istate.time_week*(86400*7*(uint64_t)1000);
     timing[instance].last_message_time_ms = tnow;
     timing[instance].last_fix_time_ms = tnow;
     _type[instance].set(GPS_TYPE_HIL);