vppinfra: add const to char* params of several funcs

These functions do not need modifiable strings.
It helps with linker sections as well as C++ compatibility.
It is a good style to use const where approriate.

Type: refactor
Signed-off-by: void234@gmail.com
Change-Id: I8d1e922197b3594122296e8c1af57e0a8ec0bf3d
diff --git a/src/vppinfra/error.h b/src/vppinfra/error.h
index e0e2d47..9eae8ea 100644
--- a/src/vppinfra/error.h
+++ b/src/vppinfra/error.h
@@ -85,10 +85,9 @@
 
 #define clib_error_free(e) e = clib_error_free_vector(e)
 
-extern clib_error_t *_clib_error_return (clib_error_t * errors,
-					 any code,
-					 uword flags,
-					 char *where, char *fmt, ...);
+extern clib_error_t *_clib_error_return (clib_error_t *errors, any code,
+					 uword flags, const char *where,
+					 const char *fmt, ...);
 
 #define clib_error_return_code(e,code,flags,args...) \
   _clib_error_return((e),(code),(flags),(char *)clib_error_function,args)