net: lwip: call sys_check_timeouts and schedule on rx

Call schedule() in net_lwip_rx() to service U-Boot tasks and
actions during packet rx.

As a cleanup also move sys_check_timeouts() here and remove it from the
functions that call net_lwip_rx().

This resolves the issue of an active watchdog resetting the board on
long network activities.

Suggested-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>
diff --git a/net/lwip/net-lwip.c b/net/lwip/net-lwip.c
index abc52b3..ff4d634 100644
--- a/net/lwip/net-lwip.c
+++ b/net/lwip/net-lwip.c
@@ -14,8 +14,10 @@
 #include <lwip/etharp.h>
 #include <lwip/init.h>
 #include <lwip/prot/etharp.h>
+#include <lwip/timeouts.h>
 #include <net.h>
 #include <timer.h>
+#include <u-boot/schedule.h>
 
 /* xx:xx:xx:xx:xx:xx\0 */
 #define MAC_ADDR_STRLEN 18
@@ -285,6 +287,11 @@
 	int len;
 	int i;
 
+	/* lwIP timers */
+	sys_check_timeouts();
+	/* Other tasks and actions */
+	schedule();
+
 	if (!eth_is_active(udev))
 		return -EINVAL;