+/** \brief Add/delete NAT44 load-balancing static mapping rule
+ @param client_index - opaque cookie to identify the sender
+ @param context - sender context, to match reply w/ request
+ @param is_add - 1 if add, 0 if delete
+ @param external_addr - external IPv4 address of the service
+ @param external_port - external L4 port number of the service
+ @param protocol - IP protocol number of the service
+ @param vrf_id - internal network VRF ID
+ @param twice_nat - if 1 translate external host address and port
+ @param out2in_only - if 1 rule match only out2in direction
+ @param tag - opaque string tag
+ @param local_num - number of local network nodes
+ @param locals - local network nodes
+*/