Revise rcode in log

Rcode in log should be 255(RCODE_TIMEOUT) rather than 0 in DNS response
timeout case.

Before:
resolv  : retrying_poll: 46 retrying_poll timeout
resolv  : doQuery: rcode=0, ancount=0

After:
resolv  : retrying_poll: 46 retrying_poll timeout
resolv  : doQuery: rcode=255, ancount=0

Bug: N/A
Test: m; adb locat
Change-Id: Ibd1ce9347c10c50a73bba5e2ae859bb402960362