Accept inbound splice attempts

Since LDK Node does not support downgrades, there's no need to have
a Config parameter for accepting inbound splices. Instead, enable it by
default.

Author: jkczyz

src/config.rs

@@ -325,6 +325,7 @@ pub(crate) fn default_user_config(config: &Config) -> UserConfig {
 	user_config.manually_accept_inbound_channels = true;
 	user_config.channel_handshake_config.negotiate_anchors_zero_fee_htlc_tx =
 		config.anchor_channels_config.is_some();
+	user_config.reject_inbound_splices = false;
 
 	if may_announce_channel(config).is_err() {
 		user_config.accept_forwards_to_priv_channels = false;