MINOR: quic: Add "no-quic" global option

Add "no-quic" to "global" section to disable the use of QUIC transport protocol
by all configured QUIC listeners. This is listeners with QUIC addresses on their
"bind" lines. Internally, the socket addresses binding is skipped by
protocol_bind_all() for receivers with <proto_quic4> or <proto_quic6> as
protocol (see protocol struct).
Add information about "no-quic" global option to the documentation.

Must be backported to 2.7.
diff --git a/src/cfgparse-global.c b/src/cfgparse-global.c
index 6cc4afe..3f4c877 100644
--- a/src/cfgparse-global.c
+++ b/src/cfgparse-global.c
@@ -45,7 +45,7 @@
 	"log-tag", "spread-checks", "max-spread-checks", "cpu-map", "setenv",
 	"presetenv", "unsetenv", "resetenv", "strict-limits", "localpeer",
 	"numa-cpu-mapping", "defaults", "listen", "frontend", "backend",
-	"peers", "resolvers", "cluster-secret",
+	"peers", "resolvers", "cluster-secret", "no-quic",
 	NULL /* must be last */
 };
 
@@ -111,6 +111,12 @@
 			goto out;
 		global.tune.options &= ~GTUNE_USE_POLL;
 	}
+	else if (strcmp(args[0], "no-quic") == 0) {
+		if (alertif_too_many_args(0, file, linenum, args, &err_code))
+			goto out;
+
+		global.tune.options |= GTUNE_NO_QUIC;
+	}
 	else if (strcmp(args[0], "busy-polling") == 0) { /* "no busy-polling" or "busy-polling" */
 		if (alertif_too_many_args(0, file, linenum, args, &err_code))
 			goto out;