MINOR: stick-table: allow sc-set-gpt0 to set value from an expression

Allow the sc-set-gpt0 action to set GPT0 to a value dynamically evaluated from
its <expr> argument (in addition to the existing static <int> alternative).
diff --git a/include/types/action.h b/include/types/action.h
index 54a6f71..516ffdd 100644
--- a/include/types/action.h
+++ b/include/types/action.h
@@ -168,6 +168,7 @@
 		struct {
 			int sc;
 			long long int value;
+			struct sample_expr *expr;
 		} gpt;
 		struct track_ctr_prm trk_ctr;
 		struct {