Switch SplicePrototype feature flag to the prod feature bit

When we shipped 0.2 we used the feature bit 155 to signal splicing,
in line with what eclair was using. However, eclair was actually
using that bit to signal splicing on a previous design which is
incompatible with the current spec.

The result of this was that eclair nodes may attempt to splice
using their protocol and we'd fail to deserialize their splice
message (resulting in a reconnect, which luckily would clear their
splice attempt and return the connection to normal).

As we really need to get off of their feature bit and there's not
much reason to keep using a non-final-spec bit, we simply redefine
`SplicePrototype` to bit 63 here.

Author: TheBlueMatt

lightning-types/src/features.rs

@@ -166,15 +166,15 @@ mod sealed {
 			// Byte 6
 			ZeroConf,
 			// Byte 7
-			Trampoline | SimpleClose | SpliceProduction,
+			Trampoline | SimpleClose | SpliceProduction | SplicePrototype,
 			// Byte 8 - 16
 			,,,,,,,,,
 			// Byte 17
 			AnchorZeroFeeCommitmentsStaging,
 			// Byte 18
 			,
 			// Byte 19
-			HtlcHold | SplicePrototype,
+			HtlcHold,
 		]
 	);
 	define_context!(
@@ -195,15 +195,15 @@ mod sealed {
 			// Byte 6
 			ZeroConf | Keysend,
 			// Byte 7
-			Trampoline | SimpleClose | SpliceProduction,
+			Trampoline | SimpleClose | SpliceProduction | SplicePrototype,
 			// Byte 8 - 16
 			,,,,,,,,,
 			// Byte 17
 			AnchorZeroFeeCommitmentsStaging,
 			// Byte 18
 			,
 			// Byte 19
-			HtlcHold | SplicePrototype,
+			HtlcHold,
 			// Byte 20 - 31
 			,,,,,,,,,,,,
 			// Byte 32
@@ -722,7 +722,7 @@ mod sealed {
 		requires_htlc_hold
 	);
 	define_feature!(
-		155, // Splice prototype feature bit as listed in https://github.com/lightning/bolts/issues/605#issuecomment-877237519.
+		63, // Actually the SpliceProduction feature
 		SplicePrototype,
 		[InitContext, NodeContext],
 		"Feature flags for channel splicing.",
@@ -1441,28 +1441,16 @@ mod tests {
 			// - onion_messages
 			// - option_channel_type | option_scid_alias
 			// - option_zeroconf
-			// - option_simple_close | option_splice
-			assert_eq!(node_features.flags.len(), 20);
+			// - option_simple_close
+			assert_eq!(node_features.flags.len(), 8);
 			assert_eq!(node_features.flags[0], 0b00000001);
 			assert_eq!(node_features.flags[1], 0b01010001);
 			assert_eq!(node_features.flags[2], 0b10001010);
 			assert_eq!(node_features.flags[3], 0b00001010);
 			assert_eq!(node_features.flags[4], 0b10001000);
 			assert_eq!(node_features.flags[5], 0b10100000);
 			assert_eq!(node_features.flags[6], 0b00001000);
-			assert_eq!(node_features.flags[7], 0b00100000);
-			assert_eq!(node_features.flags[8], 0b00000000);
-			assert_eq!(node_features.flags[9], 0b00000000);
-			assert_eq!(node_features.flags[10], 0b00000000);
-			assert_eq!(node_features.flags[11], 0b00000000);
-			assert_eq!(node_features.flags[12], 0b00000000);
-			assert_eq!(node_features.flags[13], 0b00000000);
-			assert_eq!(node_features.flags[14], 0b00000000);
-			assert_eq!(node_features.flags[15], 0b00000000);
-			assert_eq!(node_features.flags[16], 0b00000000);
-			assert_eq!(node_features.flags[17], 0b00000000);
-			assert_eq!(node_features.flags[18], 0b00000000);
-			assert_eq!(node_features.flags[19], 0b00001000);
+			assert_eq!(node_features.flags[7], 0b10100000);
 		}
 
 		// Check that cleared flags are kept blank when converting back: