[MINOR] stick-table: provide a table lookup function

We'll often need to lookup a table by its name. This will change
in the future once we can resolve these names on startup.
diff --git a/include/proto/stick_table.h b/include/proto/stick_table.h
index 813b3b9..38ec9ae 100644
--- a/include/proto/stick_table.h
+++ b/include/proto/stick_table.h
@@ -46,6 +46,7 @@
 					unsigned long table_type);
 int stktable_compatible_pattern(struct pattern_expr *expr, unsigned long table_type);
 int stktable_get_data_type(char *name);
+struct proxy *find_stktable(const char *name);
 
 /* reserve some space for data type <type>. Return non-0 if OK, or 0 if already
  * allocated (or impossible type).