Assert if we're logging after final txg was set

This allowed to debug openzfs#16714, fixed in openzfs#16782.  Without assertions
added here it is difficult to figure out what logs cause the problem,
since the assertion happens in sync thread context.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Pavel Snajdr <snajpa@snajpa.net>
Co-authored-by: Alexander Motin <mav@FreeBSD.org>
Closes openzfs#16795

module/zfs/spa_history.c

@@ -390,6 +390,9 @@ spa_history_log_nvl(spa_t *spa, nvlist_t *nvl)
 		return (err);
 	}
 
+	ASSERT3UF(tx->tx_txg, <=, spa_final_dirty_txg(spa),
+	    "Logged %s after final txg was set!", "nvlist");
+
 	VERIFY0(nvlist_dup(nvl, &nvarg, KM_SLEEP));
 	if (spa_history_zone() != NULL) {
 		fnvlist_add_string(nvarg, ZPOOL_HIST_ZONE,
@@ -527,6 +530,9 @@ log_internal(nvlist_t *nvl, const char *operation, spa_t *spa,
 		return;
 	}
 
+	ASSERT3UF(tx->tx_txg, <=, spa_final_dirty_txg(spa),
+	    "Logged after final txg was set: %s %s", operation, fmt);
+
 	msg = kmem_vasprintf(fmt, adx);
 	fnvlist_add_string(nvl, ZPOOL_HIST_INT_STR, msg);
 	kmem_strfree(msg);