state: add async anchor creation.

Actually generating the anchor transaction in my implementation
requires interaction with bitcoind, which we want to be async.  So add
a callback and a new state to wait for it.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

state_types.h

@@ -19,6 +19,7 @@ enum state {
 	 */
 	STATE_OPEN_WAIT_FOR_OPEN_NOANCHOR,
 	STATE_OPEN_WAIT_FOR_OPEN_WITHANCHOR,
+	STATE_OPEN_WAIT_FOR_ANCHOR_CREATE,
 	STATE_OPEN_WAIT_FOR_ANCHOR,
 	STATE_OPEN_WAIT_FOR_COMMIT_SIG,
 	STATE_OPEN_WAITING_OURANCHOR,
@@ -220,6 +221,8 @@ enum state_input {
 	/*
 	 * Bitcoin events
 	 */
+	/* Bitcoin anchor tx created. */
+	BITCOIN_ANCHOR_CREATED,
 	/* It reached the required depth. */
 	BITCOIN_ANCHOR_DEPTHOK,
 	/* It didn't reach the required depth in time. */