obmc-console: Provide a default value for `console-id`.

4e7186918599 ("Fixed broken dbus interface for multiple consoles")
introduced the requirement that `console-id` be specified in the
configuration files for both the client and server. It was paired with a
fix to platform configurations in the OpenBMC bitbake metadata[1]. In
theory this should have worked, but because specifying `console-id`
wasn't a requirement, not all platforms supplied a client configuration.
Instead they relied on the default behaviour.

[1]: https://gerrit.openbmc.org/c/openbmc/openbmc/+/62712

Remove the requirement that a `console-id` be specified and instead
provide a default value that can be overridden by configuration. This
carries forward the consequence from 4e7186918599 ("Fixed broken dbus
interface for multiple consoles") that the original `\0obmc-console`
abstract socket will never be created. This doesn't resolve the break in
ipmid or bmcweb, but resolves the break to SSH-based SOL on platforms
not supplying client configuration files for one of their consoles.

The fix to bmcweb (whose strategy can also be applied to ipmid) is
currently being prototyped[2].

[2]: https://discord.com/channels/775381525260664832/1083551792094249051/1103867159412752424

A deeper treatment of the problems, impacts, and solutions is provided
in [3].

[3]: https://amboar.github.io/notes/2023/05/08/happenings-in-obmc-console.html

Fixes: 4e7186918599 ("Fixed broken dbus interface for multiple consoles")
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I970578f1b695f729f6524c4da6bba6e89bf14d52
diff --git a/console-server.c b/console-server.c
index c73ebb7..0a0477d 100644
--- a/console-server.c
+++ b/console-server.c
@@ -409,11 +409,6 @@
 		}
 	}
 
-	if (!resolved_id) {
-		warnx("console-id was not specified");
-		return EXIT_FAILURE;
-	}
-
 	console->console_id = resolved_id;
 
 	/* Get the socket name/path */
diff --git a/console-socket.c b/console-socket.c
index e78cfe0..d535182 100644
--- a/console-socket.c
+++ b/console-socket.c
@@ -16,6 +16,7 @@
 
 #include "console-server.h"
 
+#include <err.h>
 #include <errno.h>
 #include <limits.h>
 #include <stdio.h>
@@ -32,14 +33,12 @@
 {
 	ssize_t rc;
 
-	if (id) {
-		rc = snprintf(sun_path + 1, sizeof(socket_path_t) - 1,
-			      CONSOLE_SOCKET_PREFIX ".%s", id);
-	} else {
-		rc = snprintf(sun_path + 1, sizeof(socket_path_t) - 1,
-			      CONSOLE_SOCKET_PREFIX);
+	if (!id) {
+		id = "default";
 	}
 
+	rc = snprintf(sun_path + 1, sizeof(socket_path_t) - 1,
+		      CONSOLE_SOCKET_PREFIX ".%s", id);
 	if (rc < 0) {
 		return rc;
 	}