Fix compilation warnings with gcc.

include/coap/net.h

@@ -565,4 +565,6 @@ coap_pdu_t *coap_wellknown_response(coap_context_t *context,
                                     coap_session_t *session,
                                     coap_pdu_t *request);
 
+unsigned int calc_timeout(unsigned char r);
+
 #endif /* _COAP_NET_H_ */

src/coap_session.c

@@ -134,8 +134,6 @@ ssize_t coap_session_send(coap_session_t *session, const uint8_t *data, size_t d
   return bytes_written;
 }
 
-unsigned int calc_timeout(unsigned char r);
-
 ssize_t
 coap_session_delay_pdu(coap_session_t *session, coap_pdu_t *pdu,
                        coap_queue_t *node)

src/coap_tinydtls.c

@@ -19,7 +19,7 @@
 #include <tinydtls.h>
 #include <dtls.h>
 
-static coap_time_t dtls_tick_0 = 0;
+static dtls_tick_t dtls_tick_0 = 0;
 static coap_tick_t coap_tick_0 = 0;
 
  /* Prototypes from dtls_debug.h as including that header will conflict
@@ -367,6 +367,7 @@ coap_dtls_hello(coap_session_t *session,
 }
 
 unsigned int coap_dtls_get_overhead(coap_session_t *session) {
+  (void)session;
   return 13 + 8 + 8;
 }