readsb's --net-bind-address is not configurable / does not listen on IPv6

[duckfullstop]

I appreciate this is probably a little more of an edge case, but I'm rocking docker-readsb-protobuf on an IPv6-first Kubernetes cluster. As services are advertised primarily by their IPv6 address, and this container forcibly sets --net-bind-address to 0.0.0.0 (the IPv4 catchall), anything that tries to dial this container over IPv6 just gets turned away at the door.

Simple proposed solution: Make READSB_NET_BIND_ADDRESS a configurable value overruling this line here:

docker-readsb-protobuf/rootfs/etc/s6-overlay/scripts/readsb

Line 14 in ff0d464

READSB_CMD=("--net-bind-address=0.0.0.0")

and potentially consider setting the default to ::, as almost all systems should tolerate it (?), and it should also bind to the wildcard v4 address at the same time.

(if readsb doesn't support binding to :: then by all means close this issue - that's the main reason I haven't done a PR!)