MINOR: mux/connection: add a new mux flag for HOL risk

This flag is used to indicate if the mux protocol is subject to
head-of-line blocking problem.

include/haproxy/connection-t.h

@@ -281,6 +281,7 @@ enum {
 	MX_FL_NONE        = 0x00000000,
 	MX_FL_CLEAN_ABRT  = 0x00000001, /* abort is clearly reported as an error */
 	MX_FL_HTX         = 0x00000002, /* set if it is an HTX multiplexer */
+	MX_FL_HOL_RISK    = 0x00000004, /* set if the protocol is subject the to head-of-line blocking on server */
 };
 
 /* PROTO token registration */

src/mux_fcgi.c

@@ -4178,7 +4178,7 @@ static const struct mux_ops mux_fcgi_ops = {
 	.ctl           = fcgi_ctl,
 	.show_fd       = fcgi_show_fd,
 	.takeover      = fcgi_takeover,
-	.flags         = MX_FL_HTX,
+	.flags         = MX_FL_HTX|MX_FL_HOL_RISK,
 	.name          = "FCGI",
 };
 

src/mux_h2.c

@@ -6219,7 +6219,7 @@ static const struct mux_ops h2_ops = {
 	.ctl = h2_ctl,
 	.show_fd = h2_show_fd,
 	.takeover = h2_takeover,
-	.flags = MX_FL_CLEAN_ABRT|MX_FL_HTX,
+	.flags = MX_FL_CLEAN_ABRT|MX_FL_HTX|MX_FL_HOL_RISK,
 	.name = "H2",
 };