shadow_server: allow specifying IP addresses to listen on (#6050)

shadow_server: allow specifying IP addresses to listen on (#6050)

* shadow_server: allow specifying IP addresses to listen on

This allows using IPv6 as well as listening only on specific
interfaces. Additionally, it enables listening on local and TCP
sockets simultaneously.

* listener: log address with square brackets

This disambiguates IPv6 addresses.

* shadow_server: check error on each socket binding

* Refactored shadow /bind-address for 2.0 compiatibility.

* Made /ipc-socket and /bind-address incompatible arguments.

* Fixed shadow /bind-address handling and description

* Allow multiple bind addresses for shadow server.

Co-authored-by: akallabeth <akallabeth@posteo.net>