evio: rework `evio_service` structure

Previosly `evio_service` was a structure, which encapsulated the
work with only one socket. Now this structure contains the array
of structs `evio_service_entry` (which work same as previously work
`evio_service`). So now struct `evio_service` encapsulates work
with any count of sockets.

Part of #3554