qcacmn: Add SYS_MSG_ID_UMAC_STOP system message

Add SYS_MSG_ID_UMAC_STOP to allow umac close to be done in
mc thread context.

Change-Id: I11946ce7aa21ce96f71d604244b9981dcae9704a
CRs-Fixed: 2156189

scheduler/inc/scheduler_api.h

@@ -55,6 +55,7 @@ typedef enum {
 	SYS_MSG_ID_FTM_RSP,
 	SYS_MSG_ID_QVIT,
 	SYS_MSG_ID_DATA_STALL_MSG,
+	SYS_MSG_ID_UMAC_STOP,
 } SYS_MSG_ID;
 
 /**