cpp: ex2: add solution

c/ex3.c

@@ -26,7 +26,7 @@ void reverse_bytes(unsigned char* buf, size_t n) {
         buf[i] = reverse_byte(buf[i]);
     }
 
-    for (size_t i = 0; i < ((n + 1) / 2); ++i) {
+    for (size_t i = 0; i <= (n / 2); ++i) {
         swap_bytes(&buf[i], &buf[n - 1 - i]);
     }
 }