net/slirp: Improve file open error message

This error reports failure to create a temporary file, and
error_setg_file_open() would probably be too terse, so merely switch
to error_setg_errno() to add errno information.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20251121121438.1249498-12-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

net/slirp.c

@@ -1034,8 +1034,10 @@ static int slirp_smb(SlirpState* s, const char *exported_dir,
 
     f = fopen(smb_conf, "w");
     if (!f) {
+        int eno = errno;
+
         slirp_smb_cleanup(s);
-        error_setg(errp,
+        error_setg_errno(errp, eno,
                    "Could not create samba server configuration file '%s'",
                     smb_conf);
         g_free(smb_conf);