[cxx]: fixed extern "C" declarations

* Moving #includes above
  #ifdef __cplusplus extern "C" { #endif
  So that we can compile with CPP.

Signed-off-by: Jakob Hasse <jakob.hasse@espressif.com>

Merges https://github.com/espressif/esp-idf/pull/6634

components/esp_adc_cal/include/esp_adc_cal.h

@@ -15,14 +15,14 @@
 #ifndef __ESP_ADC_CAL_H__
 #define __ESP_ADC_CAL_H__
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <stdint.h>
 #include "esp_err.h"
 #include "driver/adc.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /**
  * @brief Type of calibration value used in characterization
  */