client.c: show outgoing and received PDUs in log level INFO
client.c: show outgoing and received PDUs in log level INFO

coap-client now prints PDUs that are sent and received in log level
INFO so that these are output with '-v6' or higher. These messages
are now visible without turning on the full debug.

authmillenon/libcoap,authmillenon/libcoap,authmillenon/libcoap