Bugfix/ipv6 leave multicast on foreign device registration (#899)

* Fixed IPv6 handler to ignore original-broadcast when registered as a foreign-device

* Fixed IPv6 to leave multicast when registering as foreign device.

test/bacnet/basic/bbmd6/src/main.c

@@ -97,6 +97,14 @@ int bip6_send_mpdu(
     return 0;
 }
 
+/**
+ * @brief Leave a multicast group
+ */
+void bip6_leave_group(void)
+{
+    return;
+}
+
 /** Return the Object Instance number for our (single) Device Object.
  * This is a key function, widely invoked by the handler code, since
  * it provides "our" (ie, local) address.