netd: set CLOEXEC on inherited /dev/socket/netd fd

Test: on aosp_blueline no longer see iptables/ip6tables/dnsmasq/clatd with open
  /dev/system/netd fd which matches environment variable ANDROID_SOCKET_netd=18.
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I7dd4f53751dd36c15aa8cb9ee1651b93cffa4745
1 file changed