unit-tests: Seed chunk_hash() only once, but before creating any hashtables

Due to the removal of pthread_once, we manually create the seed for
chunk_hash(). With the new testable functions interface, this won't work for
the hashtable initiated using __attribute__((constructor)). Enforce seeding
before creating that hashtable.

src/libstrongswan/utils/chunk.c

@@ -917,10 +917,17 @@ static u_char static_key[] = {0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
  */
 void chunk_hash_seed()
 {
+	static bool seeded = FALSE;
 	ssize_t len;
 	size_t done = 0;
 	int fd;
 
+	if (seeded)
+	{
+		/* just once to have the same seed during the whole process lifetimes */
+		return;
+	}
+
 	fd = open("/dev/urandom", O_RDONLY);
 	if (fd >= 0)
 	{
@@ -944,6 +951,7 @@ void chunk_hash_seed()
 			key[done] = (u_char)random();
 		}
 	}
+	seeded = TRUE;
 }
 
 /**