pkg: lwip: remove timeout timer

In case of no timeout this timer is not removed, leading to the
re-addition in a later call. This fix removes it properly.

pkg/lwip/contrib/netdev2/lwip_netdev2.c

@@ -46,7 +46,6 @@
 #define ETHERNET_IFNAME1 'E'
 #define ETHERNET_IFNAME2 'T'
 
-/* running number for different interfaces */
 static kernel_pid_t _pid = KERNEL_PID_UNDEF;
 static char _stack[LWIP_NETDEV2_STACKSIZE];
 static msg_t _queue[LWIP_NETDEV2_QUEUE_LEN];

pkg/lwip/contrib/sys_arch.c

@@ -147,6 +147,7 @@ u32_t sys_arch_mbox_fetch(sys_mbox_t *mbox, void **msg, u32_t timeout)
     }
     mbox_get(&mbox->mbox, &m);
     stop = xtimer_now64();
+    xtimer_remove(&timer);  /* in case timer did not time out */
     switch (m.type) {
         case _MSG_SUCCESS:
             *msg = m.content.ptr;