ovn-northd-ddlog: Fix memory leaks.

ddlog_delta_get_table() returns data that must be freed, but the code
in northd_update_probe_interval() did not do that.  This fixes it.

In addition, the accumulated deltas weren't freed when the daemon exits.
This doesn't really matter but it's cleaner to do so, so this commit
also does that.

Signed-off-by: Ben Pfaff <blp@ovn.org>
Reported-by: Numan Siddique <numans@ovn.org>
Acked-by: Numan Siddique <numans@ovn.org>

northd/ovn-northd-ddlog.c

@@ -577,6 +577,7 @@ northd_update_probe_interval(struct northd_ctx *nb, struct northd_ctx *sb)
     table_id tid = ddlog_get_table_id("Northd_Probe_Interval");
     ddlog_delta *probe_delta = ddlog_delta_get_table(delta, tid);
     ddlog_delta_enumerate(probe_delta, northd_update_probe_interval_cb, (uintptr_t) &probe_interval);
+    ddlog_free_delta(probe_delta);
 
     ovsdb_cs_set_probe_interval(nb->cs, probe_interval);
     ovsdb_cs_set_probe_interval(sb->cs, probe_interval);
@@ -1230,6 +1231,7 @@ main(int argc, char *argv[])
     northd_ctx_destroy(nb_ctx);
     northd_ctx_destroy(sb_ctx);
 
+    ddlog_free_delta(delta);
     ddlog_stop(ddlog);
 
     if (replay_fd >= 0) {