time: import IANA timezone definitions, expose SNTP API (#6373)

* time: import IANA timezone definitions
- `configTime("timezone", "ntp servers...")` added
- timezone definitions by country/cities (TZ.h)
- script to update timezone definitions
- updated example

* fix former configTime non-matching signature

* +include

* example: add scheduled function in callback

* crlf fix

* +missing license for napt

* SNTP: expose configuration helpers

* update submodule

* update precompiled libraries

* optional: change SNTP startup delay

* makes SNTP_UPDATE_DELAY a weak function
update example
fix for lwip1.4

* on the proper use of polledTimeout api... thanks @mcspr :]

* improve update script (per review)

* update lwIP submodule

* update submodule

* hide harmless shell message

* update the release process by asking first to update TZ.h
[ci skip]

* minor update in release documentation

* update in release documentation

* update in release documentation

* clarify release documentation

* fix release documentation - sorry for the noise :(

* fixes per review

* example style

* useless variable in example

* update lwip2 submodule reference, to include espressif missing declaration fixes

tools/sdk/lwip2/include/lwipopts.h

@@ -3545,6 +3545,9 @@
 #error LWIP_FEATURES must be defined
 #endif
 
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 /**
  * TCP_RANDOM_PORT: randomize port instead of simply increasing
@@ -3561,27 +3564,34 @@
 // so we do not define it. sntp server can come from dhcp server, or by
 // user.
 //#define SNTP_SERVER_ADDRESS	"pool.ntp.org"   // default
-//#define SNTP_GET_SERVERS_FROM_DHCP	// implicitely enabled by LWIP_DHCP_GET_NTP_SRV
+//#define SNTP_GET_SERVERS_FROM_DHCP        // implicitely enabled by LWIP_DHCP_GET_NTP_SRV
 
-#define SNTP_SERVER_DNS			1        // enable SNTP support DNS names through sntp_setservername / sntp_getservername
+#define SNTP_SERVER_DNS 1                   // enable SNTP support DNS names through sntp_setservername / sntp_getservername
 
 #define SNTP_SET_SYSTEM_TIME_US(t,us)	do { struct timeval tv = { t, us }; settimeofday(&tv, NULL); } while (0)
 
+#define SNTP_SUPPRESS_DELAY_CHECK 1
+#define SNTP_UPDATE_DELAY_DEFAULT 3600000   // update delay defined by a default weak function
+#define SNTP_UPDATE_DELAY sntp_update_delay_MS_rfc_not_less_than_15000()
+extern uint32_t SNTP_UPDATE_DELAY;
+
 #if LWIP_FEATURES
-// lwip-1.4 had 3 possible SNTP servers (constant was harcoded)
+// esp8266/arduino/lwip-1.4 had 3 possible SNTP servers (constant was harcoded)
 #define SNTP_MAX_SERVERS                3
 #endif
 
-// turn off random delay before sntp request
-// when SNTP_STARTUP_DELAY is not defined,
-// LWIP_RAND is used to set a delay
+// no delay by default before sntp request
+// https://github.com/esp8266/Arduino/pull/5564
 // from sntp_opts.h:
 /** According to the RFC, this shall be a random delay
  * between 1 and 5 minutes (in milliseconds) to prevent load peaks.
  * This can be defined to a random generation function,
  * which must return the delay in milliseconds as u32_t.
  */
-#define SNTP_STARTUP_DELAY              0
+#define SNTP_STARTUP_DELAY 1                // enable startup delay
+#define SNTP_STARTUP_DELAY_FUNC_DEFAULT 0   // to 0 by default via a default weak function
+#define SNTP_STARTUP_DELAY_FUNC sntp_startup_delay_MS_rfc_not_less_than_60000()
+extern uint32_t SNTP_STARTUP_DELAY_FUNC;
 
 /*
    --------------------------------------------------
@@ -3633,4 +3643,8 @@ void tcp_kill_timewait (void);
 #define MEMP_NUM_TCP_PCB_TIME_WAIT       5
 #endif
 
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
 #endif // MYLWIPOPTS_H