BUG/MINOR: http: Call XFER_DATA analyzer when HTTP txn is switched in tunnel mode

This allow a filter to start to analyze data in HTTP and to fallback in TCP when
data are tunneled.

[wt: backport desired in 1.7 - no impact right now but may impact the ability
 to backport future fixes]
diff --git a/src/proto_http.c b/src/proto_http.c
index 1ba36e7..a37e290 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -5598,6 +5598,10 @@
 		s->res.analysers &= AN_FLT_END;
 		channel_auto_close(&s->res);
 		channel_auto_read(&s->res);
+		if (txn->req.msg_state == HTTP_MSG_TUNNEL && HAS_REQ_DATA_FILTERS(s))
+			s->req.analysers |= AN_FLT_XFER_DATA;
+		if (txn->rsp.msg_state == HTTP_MSG_TUNNEL && HAS_RSP_DATA_FILTERS(s))
+			s->res.analysers |= AN_FLT_XFER_DATA;
 	}
 	else if ((txn->req.msg_state >= HTTP_MSG_DONE &&
 		  (txn->rsp.msg_state == HTTP_MSG_CLOSED || (s->res.flags & CF_SHUTW))) ||