iproto: refactor evio service configuration

 - Call listen() once per socket in the TX thread instead of doing it in
   each IPROTO thread because calling listen() more than once has no
   effect.
 - Merge evio_service_bind and evio_service_listen into one method
   named evio_service_start to match evio_service_stop.
 - Rename IPROTO_CFG_LISTEN message to IPROTO_CFG_START to match
   IPROTO_CFG_STOP and drop the binary argument because it always
   attaches to tx_binary.
 - Drop the dead evio_service_is_active check from IPROTO_CFG_START
   because the service must be inactive at this point and we have an
   assertion for that in evio_service_attach.
 - Move ERRINJ_IPROTO_CFG_LISTEN error injection to iproto_listen and
   drop the error code of iproto_send_start_msg because it should never
   fail by design.

Needed for tarantool/tarantool-ee#432

NO_DOC=refactoring
NO_TEST=refactoring
NO_CHANGELOG=refactoring