rootless podman is not able to connect to the external ipv6 network

[ranjithrajaram]

On Fedora 36 with the latest podman/slirp4netns
podman-4.2.1-2.fc36.x86_64
slirp4netns-1.2.0-0.2.beta.0.fc36.x86_64
libslirp-4.6.1-3.fc36.x86_64

To make the containers reachable within the same host using ipv6 ip address, a custom podman ipv6 network is created using the command

podman network create test --ipv6

For containers attached to the "test" network, external ipv6 communication fails while ipv4 connection to the same external host works

Reproducer steps
For Rootless container

1. podman network create test --ipv6
2. podman run -it registry.access.redhat.com/ubi8

Try to access an external httpd service which is running on a host that has ipv6 address as well

---

Current results

1. Attaching to a custom network

---

1. Starting a container by attaching to the test network

[test@atomic-test ~]$ podman run -it --network test registry.access.redhat.com/ubi8

2. IPv6 fails while ipv4 works

[root@58542c3b602e /]# curl http://[2620:52:0:4a80:5054:ff:feeb:4fab]
curl: (7) Failed to connect to 2620:52:0:4a80:5054:ff:feeb:4fab port 80: Network is unreachable

[root@58542c3b602e /]# curl http://192.168.122.120
test

2. Without attaching to a custom network

---

external Ipv6 communication works

[test@atomic-test ~]$ podman run -it registry.access.redhat.com/ubi8
[root@b96375fd1fbe /]# curl http://[2620:52:0:4a80:5054:ff:feeb:4fab]
test

[ranjithrajaram]

Additional

We can see the slirp4netns is initialized properly with --enable-ipv6 flag

test 4785 0.0 0.0 4940 3116 pts/3 S 10:00 0:00 /usr/bin/slirp4netns --disable-host-loopback --mtu=65520 --enable-sandbox --enable-seccomp --enable-ipv6 -c -r 3 --netns-type=path /run/user/1001/netns/rootless-netns-aee53bca4df15e10fffc tap0

[MartinX3]

Same issue like containers/podman#15850