MINOR: mux: Unlink ALPN and multiplexers to rather speak of mux protocols

Multiplexers are not necessarily associated to an ALPN. ALPN is a TLS extension,
so it is not always defined or used. Instead, we now rather speak of
multiplexer's protocols. So in this patch, there are no significative changes,
some structures and functions are just renamed.
diff --git a/src/mux_pt.c b/src/mux_pt.c
index 131b070..dbdd78b 100644
--- a/src/mux_pt.c
+++ b/src/mux_pt.c
@@ -215,12 +215,12 @@
 	.name = "PASS",
 };
 
-/* ALPN selection : default mux has empty name */
-static struct alpn_mux_list alpn_mux_pt =
-	{ .token = IST(""), .mode = ALPN_MODE_ANY, .side = ALPN_SIDE_BOTH, .mux = &mux_pt_ops };
+/* PROT selection : default mux has empty name */
+static struct mux_proto_list mux_proto_pt =
+	{ .token = IST(""), .mode = PROTO_MODE_ANY, .side = PROTO_SIDE_BOTH, .mux = &mux_pt_ops };
 
 __attribute__((constructor))
 static void __mux_pt_init(void)
 {
-	alpn_register_mux(&alpn_mux_pt);
+	register_mux_proto(&mux_proto_pt);
 }