ucm: add possibility to skip the UCM card completely (Linked)

We have a requirement to "hide" some hardware drivers, because
other (main) UCM configuration will refer them.

This patch use special error codes to notify the upper layers
to skip the module loading.

BugLink: https://github.com/alsa-project/alsa-ucm-conf/issues/30
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

src/pulsecore/module.h

@@ -30,6 +30,11 @@ typedef struct pa_module pa_module;
 
 #include <pulsecore/core.h>
 
+enum {
+  PA_MODULE_ERR_UNSPECIFIED = 1,
+  PA_MODULE_ERR_SKIP = 2
+};
+
 struct pa_module {
     pa_core *core;
     char *name, *argument;