We cannot use subd_req() here: replies will come out of order, and the
we should not simply assign the reponses in FIFO order.
Changelog-Fixed: lightningd: don't get confused with parallel ping commands.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
We would never complete further ping commands if we had < responses
than pings. Oops.
Fixes: #1928
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
