MINOR: muxes: Add a flag to notify a mux does not support any upgrade
MX_FL_NO_UPG flag may now be set on a multiplexer to explicitly disable
upgrades from this mux. For now, it is set on the FCGI multiplexer because
it is not supported and there is no upgrade on backend-only multiplexers. It
is also set on the H2 multiplexer because it is clearly not supported.
diff --git a/src/mux_fcgi.c b/src/mux_fcgi.c
index 780d721..ddb2a60 100644
--- a/src/mux_fcgi.c
+++ b/src/mux_fcgi.c
@@ -4240,7 +4240,7 @@
.ctl = fcgi_ctl,
.show_fd = fcgi_show_fd,
.takeover = fcgi_takeover,
- .flags = MX_FL_HTX|MX_FL_HOL_RISK,
+ .flags = MX_FL_HTX|MX_FL_HOL_RISK|MX_FL_NO_UPG,
.name = "FCGI",
};