rename LWIP_SNTP_TIMER and set it default

Signed-off-by: Huge_Dream <534463586@qq.com>
Change-Id: Ic51d736cd421053d7486bd90cf65922ca9c8538a

src/include/lwip/opt.h

@@ -3553,15 +3553,11 @@
 #define MEMP_NUM_TCPIP_MSG_LOWPOWER 10
 #endif
 
-#if LWIP_SNTP
-#define LWIP_NSTP_TIMER    2
-#else
-#define LWIP_NSTP_TIMER    0
-#endif
+#define LWIP_SNTP_TIMER    2
 
 #define LOWPOWER_TCP_TIMER 1
 
-#define MEMP_NUM_SYS_TIMEOUT_LOW (MEMP_NUM_SYS_TIMEOUT + LWIP_NSTP_TIMER + LOWPOWER_TCP_TIMER)
+#define MEMP_NUM_SYS_TIMEOUT_LOW (MEMP_NUM_SYS_TIMEOUT + LWIP_SNTP_TIMER + LOWPOWER_TCP_TIMER)
 #endif /* LWIP_LOWPOWER */
 
 #endif /* LWIP_HDR_OPT_H */