channeld: Code to implement splicing

Update the lightningd <-> channeld interface with lots of new commands to needed to facilitate spicing.

Implement the channeld splicing protocol leveraging the interactivetx protocol.

Implement lightningd’s channel_control to support channeld in its splicing efforts.

Changelog-Added: Added the features to enable splicing & resizing of active channels.

wire/fromwire.c

@@ -280,3 +280,4 @@ void fromwire_siphash_seed(const u8 **cursor, size_t *max,
 {
 	fromwire(cursor, max, seed, sizeof(*seed));
 }
+