support all ivxlan single bit flags via a single openflow rule.

Basically extend the source policy applied bit, so the field a u8
reflects a bitmask of all the flags.

enum ivxlan_extension_flags {
    IVXLAN_SPA    = 1 << 0, /* Source Policy Applied */
    IVXLAN_DPA    = 1 << 1, /* Destination Policy Applied */
    IVXLAN_LB     = 1 << 2, /* Load Balancing Enabled */
    IVXLAN_DL     = 1 << 3, /* Don't Learn inner source addr to TEP */
    IVXLAN_FE     = 1 << 4, /* Forwarding exception seen */
    IVXLAN_MCAST  = 1 << 5, /* Multicast Routing Enabled */
    IVXLAN_MARK   = 1 << 6  /* Marker for atomic counters */
};