Update wire protocol to return and process error code first.
This will make sure dns proxy operations do not stall when
an internal error happens.
Also fix a compiler warning.
Also fix a potential buffer overflow.
And use correct types (uint32_t) rather than int when reading from network.
Change-Id: I9f99c16d6fd5e9137491a4d1b293a7c78e31b9c3
06e1831f19