networkd: disable ipv4ll default routes by default

This causes machines without connectivity to hang where they would otherwise fail. Keep it
opt-in for now, but consider whether we sholud just drop it.

man/systemd.network.xml

@@ -220,7 +220,7 @@
                                         <listitem>
                                                 <para>A boolean. When true, sets up the route needed for
                                                 non-IPv4LL hosts to communicate with IPv4LL-only hosts. Defaults
-                                                to true.
+                                                to false.
                                                 </para>
                                         </listitem>
                                 </varlistentry>

src/network/networkd-network.c

@@ -79,8 +79,6 @@ static int network_load_one(Manager *manager, const char *filename) {
         if (!network->filename)
                 return log_oom();
 
-        network->ipv4ll_route = true;
-
         network->dhcp = DHCP_SUPPORT_NONE;
         network->dhcp_ntp = true;
         network->dhcp_dns = true;