Improve SNTP start/restart (#2919)

***NO_CI***

Author: antoniofagundes

src/PAL/Lwip/lwIP_Sockets.cpp

@@ -17,6 +17,7 @@ extern "C"
 #include "lwip/sockets.h"
 #include "lwip/dhcp.h"
 #include "lwip/netif.h"
+#include <lwip/apps/sntp.h>
 }
 
 int errorCode;
@@ -188,6 +189,12 @@ void LWIP_SOCKETS_Driver::Status_callback(struct netif *netif)
         PostAddressChangedContinuation.Enqueue();
     }
 
+    // need to restart SNTP client
+#if SNTP_SERVER_DNS
+    sntp_stop();
+    sntp_init();
+#endif
+
 #if !defined(BUILD_RTM)
     // lcd_printf("\f\n\n\n\n\n\nLink Update: %s\n", (netif_is_up(netif) ? "UP  " : "DOWN"));
     // lcd_printf("         IP: %d.%d.%d.%d\n", (netif->ip_addr.addr >> 0) & 0xFF,

targets/ChibiOS/_lwIP/nf_lwipthread.c

@@ -256,7 +256,12 @@ void lwipDefaultLinkUpCB(void *p)
 #endif
 
 #if SNTP_SERVER_DNS
-    sntp_init();
+    // if not using DHCP then start SNTP
+    // otherwise SNTP will be started when DHCP request succeeds
+    if (addressMode != NET_ADDRESS_DHCP)
+    {
+        sntp_init();
+    }
 #endif
 }