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/datalink/mock/src/bip6-mock.c

@@ -17,6 +17,14 @@ bool bip6_init(char *ifname)
     return ztest_get_return_value();
 }
 
+void bip6_join_group(void)
+{
+}
+
+void bip6_leave_group(void)
+{
+}
+
 void bip6_cleanup(void)
 {
 }