Prevent netd from using the libnetd_client wrappers

Netd looping connections to itself via the libnetd_client connect()
wrapper has always unintended, although it worked until now. Once we
move the resolver into netd, the frequency of connect() calls will
increase, which makes it less acceptable.

There are several ways to detect if the calling process is netd.
Checking both uid == 0 and the argv[0] == netd makes it hard for
non-system components to spoof as netd.

Test: flash a device and check that netd logs the "Skipping..." message
Test: atest netd_integration_test
Change-Id: I9506facb4aa3094b16a98a913a1e2394056ce91a