oss-fuzz: Move test from oss-fuzz repo

tests/oss-fuzz/pdu_parse_target.c

@@ -0,0 +1,11 @@
+#include <coap.h>
+
+int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
+{
+    coap_pdu_t *pdu = coap_pdu_init(0, 0, 0, size);
+    if (!pdu) return 0;
+    
+    coap_pdu_parse(COAP_PROTO_UDP, data, size, pdu);
+    coap_delete_pdu(pdu);
+    return 0;
+}