config: expose distinct accept-amp flag

This mirrors the accept-keysend flag, but also permits users to
eventually toggle off keysend separately from AMP.

lntest/node.go

@@ -210,6 +210,7 @@ type NodeConfig struct {
 	ProfilePort int
 
 	AcceptKeySend bool
+	AcceptAMP     bool
 
 	FeeURL string
 
@@ -297,6 +298,10 @@ func (cfg NodeConfig) genArgs() []string {
 		args = append(args, "--accept-keysend")
 	}
 
+	if cfg.AcceptAMP {
+		args = append(args, "--accept-amp")
+	}
+
 	if cfg.Etcd {
 		args = append(args, "--db.backend=etcd")
 		args = append(args, "--db.etcd.embedded")