htlcswitch: move hop iterator into htlcswitch/hop package

Prepares for onion blob decoding outside of htlcswitch.

htlcswitch/hop/log.go

@@ -0,0 +1,16 @@
+package hop
+
+import (
+	"github.com/btcsuite/btclog"
+)
+
+// log is a logger that is initialized with no output filters.  This
+// means the package will not perform any logging by default until the caller
+// requests it.
+var log btclog.Logger
+
+// UseLogger uses a specified Logger to output package logging info. This
+// function is called from the parent package htlcswitch logger initialization.
+func UseLogger(logger btclog.Logger) {
+	log = logger
+}