lncfg: split off protocol options into normal and legacy, normal reqs no build tag

In this commit, we split off the protocol options into a normal and
legacy sub-config. The legacy sub-config protected by a built tag, and
will only be populated if thet tag is set. Legacy options now have a
`legacy` prefix. So `--protocol.legacyonion` is now `--protocol.onion`,
and `--protocol.committweak`, is now `--protocol.legacy.committweak`.

We also create a new experimental protocol feature sub-config for newer
features that may not yet been fully complete, so they require a build
tag.

lncfg/protocol_legacy_off.go

@@ -2,27 +2,21 @@
 
 package lncfg
 
-// ProtocolOptions is a struct that we use to be able to test backwards
-// compatibility of protocol additions, while defaulting to the latest within
-// lnd, or to enable experimental protocol changes.
-type ProtocolOptions struct {
+// Legacy is a sub-config that houses all the legacy protocol options.  These
+// are mostly used for integration tests as most modern nodes shuld always run
+// with them on by default.
+type LegacyProtocol struct {
 }
 
 // LegacyOnion returns true if the old legacy onion format should be used when
 // we're an intermediate or final hop. This controls if we set the
 // TLVOnionPayloadOptional bit or not.
-func (l *ProtocolOptions) LegacyOnion() bool {
+func (l *LegacyProtocol) LegacyOnion() bool {
 	return false
 }
 
 // NoStaticRemoteKey returns true if the old commitment format with a tweaked
 // remote key should be used for new funded channels.
-func (l *ProtocolOptions) NoStaticRemoteKey() bool {
-	return false
-}
-
-// AnchorCommitments returns true if support for the the anchor commitment type
-// should be signaled.
-func (l *ProtocolOptions) AnchorCommitments() bool {
+func (l *LegacyProtocol) NoStaticRemoteKey() bool {
 	return false
 }