8f5561d694
For global addresses the out-going interface is typically decided by the forwarding information base, so _requiring_ the user to set it with `sock_dtls` is undesirable. This has the caveat, that now on `sock_udp_send()` in the `_write()` method, the sock does not know via which network interface to send a packet with a global address, but again: this is really more a task for the underlying network stack, not the sock layer.