MINOR: http: update the macro IS_HTX_STRM() to check the stream flag SF_HTX

Instead of matching on the frontend options, we now check if the flag SF_HTX is
set or not on the stream to know if it is an HTX stream or not.
diff --git a/include/proto/proto_http.h b/include/proto/proto_http.h
index eecd9a7..ef028cd 100644
--- a/include/proto/proto_http.h
+++ b/include/proto/proto_http.h
@@ -29,7 +29,7 @@
 #include <proto/channel.h>
 #include <proto/stream.h>
 
-#define IS_HTX_STRM(strm) (strm_fe(strm)->options2 & PR_O2_USE_HTX)
+#define IS_HTX_STRM(strm) ((strm)->flags & SF_HTX)
 #define IS_HTX_SMP(smp)   ((smp)->strm && IS_HTX_STRM((smp)->strm))
 
 extern struct pool_head *pool_head_uniqueid;