Fix error code of resolv_getaddrinfo and cleanup for libnetd_resolv_test

1. Address comment and fix problem of aosp/985106
2. Add test cases for 1.
3. also do the cleanup and remove some TODO

Bug: 135506574
Test: cd system/netd && atest
Change-Id: I07eb74c1e1e25f462ecebcf8d150eae746e4b200