Use ws_g_warning() for plugin registration errors.

Those should always be reported, as they indicate that a block type
plugin is trying to do something we don't allow.

We should probably have a mechanism by which ws_g_warning() messages are
logged to the standard error for command-line programs, logged to an
error message window for GUI programs, and logged to some form of system
log for daemons.  For now, it's a good way to log non-fatal errors that
should always be shown in *some* fashion, as well as to mark messages
that should be handled in the form described in the previous sentence.

Change-Id: Ieedf87fc2dd3184a4466ae69af01f799165c1b70
Reviewed-on: https://code.wireshark.org/review/27519
Reviewed-by: Guy Harris <guy@alum.mit.edu>

wiretap/pcapng.c

@@ -21,6 +21,7 @@
 #include <string.h>
 #include <errno.h>
 
+#include <wsutil/ws_printf.h>
 
 #include "wtap-int.h"
 #include "file_wrappers.h"
@@ -251,8 +252,8 @@ register_pcapng_block_type_handler(guint block_type, block_reader reader,
          * something we don't handle in that block, submit a change
          * to the main Wireshark source).
          */
-        pcapng_debug("Attempt to register plugin for block type 0x%08x not allowed",
-            block_type);
+        ws_g_warning("Attempt to register plugin for block type 0x%08x not allowed",
+                     block_type);
         return;
 
     case BLOCK_TYPE_IRIG_TS:
@@ -275,8 +276,8 @@ register_pcapng_block_type_handler(guint block_type, block_reader reader,
               * No; don't allow a plugin to be registered for it, as
               * the block type needs to be registered before it's used.
               */
-            pcapng_debug("Attempt to register plugin for reserved block type 0x%08x not allowed",
-                      block_type);
+            ws_g_warning("Attempt to register plugin for reserved block type 0x%08x not allowed",
+                         block_type);
             return;
          }