Fix issue with discovery on Android 13

[alexballas]

No description provided.

[alexballas]

Converting to draft @koron fyi
According to the following documentation

func (*ipv4.dgramOpt).JoinGroup(ifi *net.Interface, group net.Addr) error
JoinGroup joins the group address group on the interface ifi. By default all sources that can cast data to group are accepted. It's possible to mute and unmute data transmission from a specific source by using ExcludeSourceSpecificGroup and IncludeSourceSpecificGroup. JoinGroup uses the system assigned multicast interface when ifi is nil, although this is not recommended because the assignment depends on platforms and sometimes it might require routing configuration.

Passing nil to the interfaces will use the system assigned multicast interface, which seems to work fine in Android without worrying about calling net.Interfaces()

[koron]

thank you for notifying this.

i closed this pull request for two reasons.

1. android is not a primary OS which Go supports
2. looks like it can be implemented without including android-specific code