At least to notifiy an application of changed local address, these pcb types need an 'err' callback.

The current implementation for tcp-listen and udp is to silently change the address, but that doesn't work well for ipv6 and doesn't seem to match posix behaviour (where a listen socket bound to a specific address just doesn't receive further connections on address change) --> that should be changed, too (or at least be optional? - thanks to the holy grail of backwards compatibility)