MINOR: cli: make "show fd" report the mux and mux_ctx pointers when available

This is handy to quickly distinguish H2 connections as well as to easily
access the h2c context. It could be backported to 1.8 to help during
troubleshooting sessions.
diff --git a/src/cli.c b/src/cli.c
index f19b5f1..c9f2067 100644
--- a/src/cli.c
+++ b/src/cli.c
@@ -777,6 +777,8 @@
 		struct listener *li = NULL;
 		struct server *sv = NULL;
 		struct proxy *px = NULL;
+		struct mux_ops *mux = NULL;
+		void *ctx = NULL;
 		uint32_t conn_flags = 0;
 
 		fdt = fdtab[fd];
@@ -786,6 +788,8 @@
 
 		if (fdt.iocb == conn_fd_handler) {
 			conn_flags = ((struct connection *)fdt.owner)->flags;
+			mux = ((struct connection *)fdt.owner)->mux;
+			ctx = ((struct connection *)fdt.owner)->mux_ctx;
 			li = objt_listener(((struct connection *)fdt.owner)->target);
 			sv = objt_server(((struct connection *)fdt.owner)->target);
 			px = objt_proxy(((struct connection *)fdt.owner)->target);
@@ -829,6 +833,11 @@
 				chunk_appendf(&trash, " sv=%s/%s", sv->id, sv->proxy->id);
 			else if (li)
 				chunk_appendf(&trash, " fe=%s", li->bind_conf->frontend->id);
+
+			if (mux)
+				chunk_appendf(&trash, " mux=%s mux_ctx=%p", mux->name, ctx);
+			else
+				chunk_appendf(&trash, " nomux");
 		}
 		else if (fdt.iocb == listener_accept) {
 			chunk_appendf(&trash, " l.st=%s fe=%s",