net: Fix a misleading error message

The error message

    $ qemu-system-x86_64 -netdev user,id=net0,ipv6-net=fec0::0/
    qemu-system-x86_64: -netdev user,id=net0,ipv6-net=fec0::0/: Parameter 'ipv6-prefixlen' expects a number

points to ipv6-prefixlen instead of ipv6-net.  Fix:

    qemu-system-x86_64: -netdev user,id=net0,ipv6-net=fec0::0/: parameter 'ipv6-net' expects a number after '/'

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20231031111059.3407803-6-armbru@redhat.com>

net/net.c

@@ -1227,7 +1227,7 @@ static int net_client_init(QemuOpts *opts, bool is_netdev, Error **errp)
     int ret = -1;
     Visitor *v = opts_visitor_new(opts);
 
-    /* Parse convenience option format ip6-net=fec0::0[/64] */
+    /* Parse convenience option format ipv6-net=fec0::0[/64] */
     const char *ip6_net = qemu_opt_get(opts, "ipv6-net");
 
     if (ip6_net) {
@@ -1247,8 +1247,8 @@ static int net_client_init(QemuOpts *opts, bool is_netdev, Error **errp)
         if (substrings[1] &&
             qemu_strtoul(substrings[1], NULL, 10, &prefix_len))
         {
-            error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
-                       "ipv6-prefixlen", "a number");
+            error_setg(errp,
+                       "parameter 'ipv6-net' expects a number after '/'");
             goto out;
         }