sniffer functionality fixed buffer

It is possible to use sniffer.py to sniff the phone-simcard-communication.

To be fixed: The buffer size read is fixed and the data is only send
over USB if the buffer max length is reached. which means we don not
get the last bytes of the transaction.
This should be changed in one of the next commits. Maybe the former
simtrace code can give some inspiration on this topic.

sam3s_example/simtrace/simtrace.h

@@ -1,6 +1,19 @@
 #ifndef SIMTRACE_H
 #define SIMTRACE_H
 
+/* Endpoint numbers */
+#define DATAOUT     1
+#define DATAIN      2
+#define INT         3
+
+#define BUFLEN  64
+typedef struct ring_buffer
+{
+    uint8_t     buf[BUFLEN*2];   // data buffer
+    uint8_t     idx;                // number of items in the buffer
+} ring_buffer;
+
+
 enum confNum {
     CFG_NUM_SNIFF = 1, CFG_NUM_PHONE, CFG_NUM_MITM, NUM_CONF
 };