Incorrect byteorder for CAS values in OBSERVE response

The CAS values which are going in the header encoded using htonll(), but those from OBSERVE response are not

Verified as working with simple patch

result.write((char*) &keystatus, sizeof(uint8_t));

• result.write((char*) &kstats.cas, sizeof(uint64_t));
  + uint64_t tmp = htonll(kstats.cas);
  + result.write((char*) &tmp, sizeof(uint64_t));
  }