diffie-hellman: Use bool instead of status_t as get_shared_secret() return value

While such a change is not unproblematic, keeping status_t makes the API
inconsistent once we introduce return values for the public value operations.

src/libcharon/plugins/load_tester/load_tester_diffie_hellman.c

@@ -26,11 +26,11 @@ METHOD(diffie_hellman_t, set_other_public_value, void,
 {
 }
 
-METHOD(diffie_hellman_t, get_shared_secret, status_t,
+METHOD(diffie_hellman_t, get_shared_secret, bool,
 	load_tester_diffie_hellman_t *this, chunk_t *secret)
 {
 	*secret = chunk_empty;
-	return SUCCESS;
+	return TRUE;
 }
 
 METHOD(diffie_hellman_t, get_dh_group, diffie_hellman_group_t,