[esl] Add SHUTDOWN_REQUESTED event.

libs/esl/src/esl_event.c

@@ -148,6 +148,7 @@ static const char *EVENT_NAMES[] = {
 	"CALL_DETAIL",
 	"DEVICE_STATE",
 	"TEXT",
+	"SHUTDOWN_REQUESTED",
 	"ALL"
 };
 

libs/esl/src/include/esl_event.h

@@ -138,6 +138,7 @@ typedef enum {
 	ESL_EVENT_CALL_DETAIL,
 	ESL_EVENT_DEVICE_STATE,
 	ESL_EVENT_TEXT,
+	ESL_EVENT_SHUTDOWN_REQUESTED,
 	ESL_EVENT_ALL
 } esl_event_types_t;