Fix sntp_get_real_time prototype in header (#7707)

sntp_get_real_time takes a `time_t` in the core, but in the header it
was listed as `long`.  Make them both match by changing the header.

Author: earlephilhower

tools/sdk/include/sntp.h

@@ -18,7 +18,7 @@ uint32 sntp_get_current_timestamp();
 /**
  * get real time (GTM + 8 time zone)
  */
-char* sntp_get_real_time(long t);
+char* sntp_get_real_time(time_t t);
 /**
  * SNTP get time_zone default GMT + 8
  */