df: reinitialize dual-funding

Prior to this, all reconnect logic lived in channeld. If you
disconnected before we finished building a funding transaction, that was
no big deal. Now, however, we're waiting for the funding to lock in in
dualopend, instead of handing straight to channeld to wait.

So we need a way to restart dualopend.

wallet/db_postgres_sqlgen.c

@@ -1780,4 +1780,4 @@ struct db_query db_postgres_queries[] = {
 
 #endif /* LIGHTNINGD_WALLET_GEN_DB_POSTGRES */
 
-// SHA256STAMP:6ab0acf78761f626e452b9d6b83206d2546872001c93779eeb2f15ff8accd62f
+// SHA256STAMP:ca47a99b5c64139f4556f3bf77a6d984cb9ab6b38bcd2851bc551c75c5cc240a