Current application data size in echo_client sample does not fit into a
single datagram with DTLS enbled for default IPv6 MTU (1280 bytes). This
caused abrupt failure of the sample with DTLS enabled over 802.15.4 L2.
Decreasing the application data size allows it to fit into a single UDP
datagram after encapsulating it into DTLS record.
Additionally, finetune DTLS timeout on echo_server to match UDP
application timeout on echo_client (so that a single datagram loss
does not cauase DTLS session to end).
Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>
Add DTLS support to socket echo_client and echo_server samples.
Additionally, move TLS-related configs to overlay-tls.conf config file,
to align with other examples.
Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>
