ctrl: use #define for TRAP id

We always use id = 0 when sending TRAP messages. Let's make this more
obvious by introducing appropriate define.

Change-Id: I33d7d4c6a1885a75a85d6f2f017430e0860b4126

include/osmocom/ctrl/control_cmd.h

@@ -12,6 +12,7 @@
 #define CTRL_CMD_ERROR		-1
 #define CTRL_CMD_HANDLED	0
 #define CTRL_CMD_REPLY		1
+#define CTRL_CMD_TRAP_ID	"0"
 
 struct ctrl_handle;
 

src/ctrl/control_if.c

@@ -156,7 +156,7 @@ int ctrl_cmd_send_trap(struct ctrl_handle *ctrl, const char *name, char *value)
 	if (!cmd)
 		return -ENOMEM;
 
-	cmd->id = "0"; /* It's a TRAP! */
+	cmd->id = CTRL_CMD_TRAP_ID; /* It's a TRAP! */
 	cmd->variable = (char *) name;
 	cmd->reply = value;
 	r = ctrl_cmd_send_to_all(ctrl, cmd);