Refactor admin socket setup (isolated config)

src/admin/options.go

@@ -0,0 +1,16 @@
+package admin
+
+func (c *AdminSocket) _applyOption(opt SetupOption) {
+	switch v := opt.(type) {
+	case ListenAddress:
+		c.config.listenaddr = v
+	}
+}
+
+type SetupOption interface {
+	isSetupOption()
+}
+
+type ListenAddress string
+
+func (a ListenAddress) isSetupOption() {}