dlmalloc: use static magic constant for debug images

Avoids crashes on restarts if svm root region backing file was not
cleaned up.

Change-Id: I608cf5711aa8c3f9620900473bdf76bde8b918de
Signed-off-by: Florin Coras <fcoras@cisco.com>
diff --git a/src/vppinfra/dlmalloc.h b/src/vppinfra/dlmalloc.h
index b3278f9..b8e3236 100644
--- a/src/vppinfra/dlmalloc.h
+++ b/src/vppinfra/dlmalloc.h
@@ -528,6 +528,7 @@
 
 #if CLIB_DEBUG > 0
 #define FOOTERS 1  /* extra debugging */
+#define DLM_MAGIC_CONSTANT 0xdeaddabe
 #endif
 #define USE_LOCKS 1
 #define DLM_ABORT {extern void os_panic(void); os_panic(); abort();}