Script to create publically routable rootless podman networks

Usage:
  Setup public routing for podman network <name>
  Usage: setup-rootless [ -r ] <name> | -x | -h
  Options:
   -h - show help
   -r - remove (all if no <name>)

Example:

  # make kind network routable from host
  $ setup-rootless kind

  # remove kind network routes
  $ setup-rootless -r kind

  # remove interface link (and associated routes)
  $ setup-rootless -r

Default config:

  # host (and rootless) interface name
  SR_INTF=cni0

  # podman network created to reserve route ips
  SR_NET=reserved

  # rootless network namespace name
  SR_NS="${USER}-rootless"

  # pod created to pin rootless namespace
  SR_INFRA=rootless

Creates host interface $SR_INTF and routes for subnets in named podman
networks.  If $SR_NET exists, it is used to determine single vs
dual-stack networking (default: dual).  $SR_NET also determines the host
addresses for $SR_INTF and nexthop addresses for added routes.

Theory:

  The script creates a infrastructure pod named in $SR_INFRA to preserve
  the rootless namespace.

  It then attaches the podman rootless namespace to $SR_NS

  The script creates a virtual ethernet pair in the podman rootless
  network namespace, and moves one peer to the host.  The interface
  is named in $SR_INTF

  It then assigns the veth pair two "unused" network ips from
  the network named in $SR_NET, and adds a default route to the host
  peer for the rootless network.

  Finally, for any supplied podman network, it adds a host route to
  the rootless peer.

  The script is idempotent, so can be run multiple times and will
  attempt to configure the network as designed.

Requires:
  ip - to configure inet
  podman - to manage containers/networks
  jq - to parse config
  sudo - for privileged operations

sudo command patterns required (for SR_NS=devel-rootless, SR_INTF=cni0):

  ip ^netns attach devel-rootless [0-9]+$
  ip netns del devel-rootless
  ip ^-n devel-rootless link set cni0-peer name cni0 netns [^ ]+$
  ip ^addr add [0-9a-f:./]+ dev cni0$
  ip link set cni0 up
  ip ^route add [0-9a-f:./]+ via [0-9a-f:.]+ dev cni0$
  ip ^route del [0-9a-f:./]+ dev cni0$

Script is self-documented (text above is copied from the leading script
comments)