We get intermittant reports of subd->conn being leaked, but I could never find it.
That's because it's actually subd which is not referenced any more: subd->conn
gets reported because it's subd's tal_parent (and, except for the reference in
subd, not referenced either).
The real issue is that the channel->owner is reassigned to the new subdaemon,
and the old one is still exiting. During that time, we can see a "leak".
```
- Node /tmp/ltests-hkr089bp/test_sql_1/lightning-3/ has memory leaks: [
{
"backtrace": [
"ccan/ccan/tal/tal.c:477 (tal_alloc_)",
"ccan/ccan/io/io.c:91 (io_new_conn_)",
"lightningd/subd.c:774 (new_subd)",
"lightningd/subd.c:828 (new_channel_subd_)",
"lightningd/dual_open_control.c:3662 (peer_restart_dualopend)",
"lightningd/peer_control.c:1161 (connect_activate_subd)",
"lightningd/peer_control.c:1273 (peer_connected_hook_final)",
"lightningd/plugin_hook.c:213 (plugin_hook_callback)",
"lightningd/plugin.c:591 (plugin_response_handle)",
"lightningd/plugin.c:702 (plugin_read_json_one)",
"lightningd/plugin.c:747 (plugin_read_json)",
"ccan/ccan/io/io.c:59 (next_plan)",
"ccan/ccan/io/io.c:407 (do_plan)",
"ccan/ccan/io/io.c:417 (io_ready)",
"ccan/ccan/io/poll.c:453 (io_loop)",
"lightningd/io_loop_with_timers.c:22 (io_loop_with_timers)",
"lightningd/lightningd.c:1249 (main)"
],
"label": "ccan/ccan/io/io.c:91:struct io_conn",
"parents": [
"lightningd/lightningd.c:107:struct lightningd"
],
"value": "0x556c63c859f8"
}
```
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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