[TWAMP] Corrections in TWAMP-test packet
[TWAMP][timestamp] NTP time + arguments is pointer

Many function arguments were changed to pointer to constant struct.
Time in timestamp now NTP.
[TWAMP][client] Many little corrections

Messages counters now uint32_t, session counters uint16_t, sequence
number and error estimate set to network byte order.
[TWAMP][server] Little corrections

Packets now may be shorter that 41 byte, sequence number  and error
estimate in network byte order.