navigation.h handle mission item structure padding explicitly

- also applies to mission_stats_entry_s, mission_fence_point_s,
   mission_save_point_s
 - -Wpadded warning is disabled by default because the snapdragon
   toolchain doesn't respect the pragma pop

src/modules/dataman/dataman.h

@@ -99,7 +99,7 @@ struct dataman_compat_s {
 };
 
 /* increment this define whenever a binary incompatible change is performed */
-#define DM_COMPAT_VERSION	1ULL
+#define DM_COMPAT_VERSION	2ULL
 
 #define DM_COMPAT_KEY ((DM_COMPAT_VERSION << 32) + (sizeof(struct mission_item_s) << 24) + \
 		       (sizeof(struct mission_s) << 16) + (sizeof(struct mission_stats_entry_s) << 12) + \