A sprinkling of const in vlibmemory/api.h and friends

Change-Id: I953ebb37eeec7de0c4a6b00258c3c67a83cbc020
Signed-off-by: Neale Ranns <nranns@cisco.com>
diff --git a/src/svm/svmdb.h b/src/svm/svmdb.h
index e02628a..e35be8a 100644
--- a/src/svm/svmdb.h
+++ b/src/svm/svmdb.h
@@ -83,7 +83,7 @@
 
 typedef struct
 {
-  char *root_path;
+  const char *root_path;
   uword size;
   u32 uid;
   u32 gid;