net: lwip: use timer_early_get_count() when CONFIG_SANDBOX_TIMER=y

When the sandbox timer is available, use it. This allows skipping
time in the tests (sandbox_eth_skip_timeout()).

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
(cherry picked from commit bebe7fe3ee)

net/lwip/net-lwip.c

@@ -13,6 +13,7 @@
 #include <lwip/init.h>
 #include <lwip/prot/etharp.h>
 #include <net.h>
+#include <timer.h>
 
 /* xx:xx:xx:xx:xx:xx\0 */
 #define MAC_ADDR_STRLEN 18
@@ -325,7 +326,11 @@ int net_loop(enum proto_t protocol)
 
 u32_t sys_now(void)
 {
+#if CONFIG_IS_ENABLED(SANDBOX_TIMER)
+	return timer_early_get_count();
+#else
 	return get_timer(0);
+#endif
 }
 
 int net_start_again(void)