Add FC17 Read Server ID (0x11)

[aldas]

This PR adds FC17 (0x11) Read Server ID, Requested by aldas/modbus-tcp-client#55 (comment)

// ReadServerIDRequestRTU is RTU Request for Read Server ID function (FC=17, 0x11)
//
// Example packet:  0x10 0x11 0xcc 0x7c
// 0x10 - unit id (0)
// 0x11 - function code (1)
// 0xcc 0x7c - CRC16 (6,7)

// ReadServerIDResponseRTU is RTU Response for Read Server ID (FC=17) 0x11
//
// Example packet: 0x10 0x11 0x02 0x01 0x02 0x00 0x01 0x02 0xd5 0x43
// 0x10 - unit id (0)
// 0x11 - function code (1)
// 0x02 - byte count for server id (2)
// 0x01 0x02 - N bytes for server id (device specific, variable length) (3,4)
// 0x00 - run status (5)
// 0x01 0x02 - optional N bytes for additional data (device specific, variable length) (6,7)
// 0xd5 0x43 - CRC16 (n-2,n-1)