SMS smpp relay options

There are a number of options under.

See also:
 * listen_receive_timeout Option
 * listen_transmit_timeout Option
 * make_source_addresses_unique Option
 * server_host Option
 * server_port Option
 * server_receive_timeout Option
 * server_transmit_timeout Option
 * max_conns Option
 * tcp_ports Option
 * listen_addresses Option
 * backlog Option
 * SMS options