samples: net: sockets: coap_server: Switch to IPv6 by default

The documentation of the sample refers IPv6 instead of IPv4.
Additionally, the coexisting coap_client sample also uses IPv6 by
default. Therefore, switch the sample default configuration to use IPv6
instead of IPv4.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>
1 file changed