Add probabilistic use of TCP_FASTOPEN and close()

rand.h

@@ -1,7 +1,9 @@
 #pragma once
 
+#include <stdbool.h>
 #include <stddef.h>
 
 void rand_init(void);
 void rand_cleanup(void);
 void rand_fill(void *, size_t);
+bool rand_yes_no(uint64_t);