bgpd: Fix compile failure if IPv6 build was disabled.

* bgp_route.c: ({no_,}ipv6_bgp_network_ttl_cmd) depends on ipv6_bgp_network
  which is HAVE_IPV6, so these should be too.
  (bgp_route_init) and the installs should be similarly ifdefed
diff --git a/bgpd/bgp_route.c b/bgpd/bgp_route.c
index 7a57e13..cfaf1b6 100644
--- a/bgpd/bgp_route.c
+++ b/bgpd/bgp_route.c
@@ -4327,6 +4327,7 @@
        "Specify a BGP backdoor route\n"
        "AS-Path hopcount limit attribute\n"
        "AS-Pathlimit TTL, in number of AS-Path hops\n")
+#ifdef HAVE_IPV6
 ALIAS_DEPRECATED (ipv6_bgp_network,
        ipv6_bgp_network_ttl_cmd,
        "network X:X::X:X/M pathlimit <0-255>",
@@ -4342,6 +4343,7 @@
        "IPv6 prefix <network>/<length>\n"
        "AS-Path hopcount limit attribute\n"
        "AS-Pathlimit TTL, in number of AS-Path hops\n")
+#endif /* HAVE_IPV6 */
 
 /* Aggreagete address:
 
@@ -12096,9 +12098,11 @@
   install_element (BGP_IPV4M_NODE, &no_bgp_network_backdoor_ttl_cmd);
   install_element (BGP_IPV4M_NODE, &no_bgp_network_mask_backdoor_ttl_cmd);
   install_element (BGP_IPV4M_NODE, &no_bgp_network_mask_natural_backdoor_ttl_cmd);
-  
+
+#ifdef HAVE_IPV6
   install_element (BGP_IPV6_NODE, &ipv6_bgp_network_ttl_cmd);
   install_element (BGP_IPV6_NODE, &no_ipv6_bgp_network_ttl_cmd);
+#endif
 }
 
 void