Fix compile of test_tcp.c unit test after introduction of tcp_next_iss hook
diff --git a/test/unit/tcp/test_tcp.c b/test/unit/tcp/test_tcp.c
index bfcfa1d..8195346 100644
--- a/test/unit/tcp/test_tcp.c
+++ b/test/unit/tcp/test_tcp.c
@@ -35,8 +35,8 @@
 {
   /* reset iss to default (6510) */
   tcp_ticks = 0;
-  tcp_ticks = 0 - (tcp_next_iss() - 6510);
-  tcp_next_iss();
+  tcp_ticks = 0 - (tcp_next_iss(NULL) - 6510);
+  tcp_next_iss(NULL);
   tcp_ticks = 0;
 
   test_tcp_timer = 0;
@@ -513,8 +513,8 @@
 
   /* create and initialize the pcb */
   tcp_ticks = 0;
-  tcp_ticks = 0 - tcp_next_iss();
-  tcp_ticks = SEQNO1 - tcp_next_iss();
+  tcp_ticks = 0 - tcp_next_iss(NULL);
+  tcp_ticks = SEQNO1 - tcp_next_iss(NULL);
   pcb = test_tcp_new_counters_pcb(&counters);
   EXPECT_RET(pcb != NULL);
   EXPECT(pcb->lastack == SEQNO1);