FIX IPv4-ONLY AsyncUDP::listenMulticast() for receiving IPv6

[nikiwaibel]

Description of Change

AsyncUDP::listenMulticast() properly receives packets sent to IPv4 multicast addresses like 239.1.2.3, but it is not receiving packets sent to IPv6 multicast addresses like ff12::6ood:cafe.

The root cause is a bit hidden: listen(NULL, port) would match AsyncUDP::listen(const ip_addr_t *addr, uint16_t port), which calls _udp_bind(_pcb, addr, port), which uses the lwIP API to call udp_bind(struct udp_pcb *pcb, const ip_addr_t *ipaddr, u16_t port) at the end. If lwIP has LWIP_IPV4 enabled, it checks if ipaddr == NULL and sets it to IP4_ADDR_ANY. So an IPv6 address is never bound.

This fix checks the IP address passed to AsyncUDP::listenMulticast(). If it is an IPv6 address, it constructs and passes the IPv6 any address (::); otherwise (IPv4), it constructs and passes the IPv4 any address (0.0.0.0).

Tests scenarios

Heltec v3

Related links

Fix #9970

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⚠️	The source branch "FIX-AsyncUDP-multicast-IPv4ONLY" incorrect format: contains uppercase letters. This can cause troubles on case-insensitive file systems (macOS). Please rename your branch.

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