Unified attribute and filter types

This commit removes the EAF_TYPE_* namespace completely and also for
route attributes, filter-based types T_* are used. This simplifies
fetching and setting route attributes from filters.

Also, there is now union bval which serves as an universal value holder
instead of private unions held separately by eattr and filter code.

filter/filter.h

@@ -77,6 +77,6 @@ struct custom_attribute {
   const char *name;
 };
 
-struct custom_attribute *ca_lookup(pool *p, const char *name, int ea_type);
+struct custom_attribute *ca_lookup(pool *p, const char *name, btype type);
 
 #endif