pdt: Added check if already defined

TRUE and FALSE is also defined in net-snmp library. Without this check,
compilation and includes must be made in a certain order.

Signed-off-by: Anders Selhammer <anders.selhammer@est.tech>

pdt.h

@@ -22,7 +22,12 @@
 
 #include <stdint.h>
 
-enum {FALSE, TRUE};
+#ifndef FALSE
+#define FALSE	0
+#endif
+#ifndef TRUE
+#define TRUE	1
+#endif
 
 typedef	int       Boolean;
 typedef uint8_t   Enumeration8;