Improve netd detection

The alleged improvement consists in making the detection actually work
when netd is spawned by init, which of course uses the full path.
I had tested the previous logic by running netd from the shell, which
worked because argv[0] was just set to "netd". My bad -_-

Test: flash, boot and grep logcat for "Skipping libnetd_client init"
Change-Id: Ie5f11436dfa2a9347721147dc2b980144452404a