Use posix_spawn instead of vfork

Also correct usage of posix_spawn

Bug: 126128460
Test: built, flashed, booted
      system/netd/tests/runtests.sh pass
      manual test with remove dnsmasq, netd works fine

Change-Id: Id48c7bf9c02ea27d3a4602efa3913785c0d5c87f
2 files changed