df: add needed info to any PSBT we produce

dual funding needs the max-witness-len and utxo fields set for every
input. we should add them when we create a 'fundpsbt', so that every
psbt that c-lightning generates is dual-funding ready

devtools/Makefile

@@ -33,6 +33,7 @@ DEVTOOLS_COMMON_OBJS :=				\
 	common/memleak.o			\
 	common/node_id.o			\
 	common/per_peer_state.o			\
+	common/psbt_open.o			\
 	common/pseudorand.o			\
 	common/json.o				\
 	common/json_helpers.o			\