Fix ipv6 options according to documentation

The options names were fixed in the qapi layer, but not in the command-line
options.
Signed-off-by: NSamuel Thibault <samuel.thibault@ens-lyon.org>
Reviewed-by: NEric Blake <eblake@redhat.com>

net/net.c

@@ -1054,32 +1054,32 @@ int net_client_init(QemuOpts *opts, int is_netdev, Error **errp)
 
     {
         /* Parse convenience option format ip6-net=fec0::0[/64] */
-        const char *ip6_net = qemu_opt_get(opts, "ip6-net");
+        const char *ip6_net = qemu_opt_get(opts, "ipv6-net");
 
         if (ip6_net) {
             char buf[strlen(ip6_net) + 1];
 
             if (get_str_sep(buf, sizeof(buf), &ip6_net, '/') < 0) {
                 /* Default 64bit prefix length.  */
-                qemu_opt_set(opts, "ip6-prefix", ip6_net, &error_abort);
-                qemu_opt_set_number(opts, "ip6-prefixlen", 64, &error_abort);
+                qemu_opt_set(opts, "ipv6-prefix", ip6_net, &error_abort);
+                qemu_opt_set_number(opts, "ipv6-prefixlen", 64, &error_abort);
             } else {
                 /* User-specified prefix length.  */
                 unsigned long len;
                 int err;
 
-                qemu_opt_set(opts, "ip6-prefix", buf, &error_abort);
+                qemu_opt_set(opts, "ipv6-prefix", buf, &error_abort);
                 err = qemu_strtoul(ip6_net, NULL, 10, &len);
 
                 if (err) {
                     error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
-                              "ip6-prefix", "a number");
+                              "ipv6-prefix", "a number");
                 } else {
-                    qemu_opt_set_number(opts, "ip6-prefixlen", len,
+                    qemu_opt_set_number(opts, "ipv6-prefixlen", len,
                                         &error_abort);
                 }
             }
-            qemu_opt_unset(opts, "ip6-net");
+            qemu_opt_unset(opts, "ipv6-net");
         }
     }