For macOS, we want to set the DF bit for the UDP packets used by the QUIC
connection; to achieve this, you need to explicitly set the network
to either "udp4" or "udp6". When determining which network type to pick
we need to use the edge IP address chosen to align with what the local
IP family interface we will use. This means we want cloudflared to bind
to local interfaces for a random port, so we provide a zero IP and 0 port
number (ex. 0.0.0.0:0). However, instead of providing the zero IP, we
can leave the value as nil and let the kernel decide which interface and
pick a random port as defined by the target edge IP family.
This was previously broken for IPv6-only edge connectivity on macOS and
all other operating systems should be unaffected because the network type
was left as default "udp" which will rely on the provided local or remote
IP for selection.
Closes TUN-8688
Devin Carr
Areg Harutyunyan