core: Add a new hook PA_CORE_HOOK_CARD_PROFILE_CHANGED

This will allow modules to know when a card profile has changed
and take appropriate action. This might prove useful when developing
UCM so that the appropriate verb can be set.

src/pulsecore/card.c

@@ -241,6 +241,8 @@ int pa_card_set_profile(pa_card *c, const char *name, pa_bool_t save) {
     c->active_profile = profile;
     c->save_profile = save;
 
+    pa_hook_fire(&c->core->hooks[PA_CORE_HOOK_CARD_PROFILE_CHANGED], c);
+
     return 0;
 }