Due to all the changes, this is basically a new version for this
example. The main benefit is the use of sock_udp but also the client
side is now more robust and reliable.
The parameters required for the PSK and ECC (e.g. keys) modes are moved
to an unique header.
The NIB's forwarding engine behaves more correctly than GNRC's old
forwarding engine in that link-local addresses require also an
interface to be provided to be meaningful. As with other commands this
is simplified for the special case that there only is one interface
that that interface is chosen.
