Fix entries in /etc/hosts disabling static leases.

It is possible for a config entry to have one address family specified by a
dhcp-host directive and the other added from /etc/hosts. This is especially
common on OpenWrt because it uses odhcpd for DHCPv6 and IPv6 leases are
imported into dnsmasq via a hosts file.

To handle this case there need to be separate *_HOSTS flags for IPv4 and IPv6.
Otherwise when the hosts file is reloaded it will clear the CONFIG_ADDR(6) flag
which was set by the dhcp-host directive.

src/dnsmasq.h

@@ -789,6 +789,7 @@ struct dhcp_config {
 #define CONFIG_BANK           2048    /* from dhcp hosts file */
 #define CONFIG_ADDR6          4096
 #define CONFIG_WILDCARD       8192
+#define CONFIG_ADDR6_HOSTS   16384    /* address added by from /etc/hosts */
 
 struct dhcp_opt {
   int opt, len, flags;