Issue: udp_sendto() Fails for multicast IPV6 packet when interface is switched from SoftAP to STA mode.
When SoftAP start is called, add_ethernet_interface() will be called internally to add interface details into netif_list.
When switching from SoftAP to STA mode, add_ethernet_interface() will be called again to append the interace details into netif_list.
When udp_sendto() is called, ip6_route() will return interface as NULL since it consider device as single interface.
Fix: SoftAP mode Stop, call remove_ethernet_interface() to remove the interface from the netif_list.
Arun S
Ryan Morse