Enable SELinux protections for netd.

This change does several things:

1) Restore domain.te to the version present at
cd516a32 . This is the version
currently being distributed in AOSP.

2) Add "allow domain properties_device:file r_file_perms;" to
domain.te, to allow all domains to read /dev/__properties__ .
This change was missing from AOSP.

3) Restore netd.te to the version present at
80c9ba52 . This is the version
currently being distributed in AOSP.

4) Remove anything involving module loading from netd.te. CTS
enforces that Android kernels can't have module loading enabled.

5) Add several new capabilities, plus data file rules, to
netd.te, since netd needs to write to files owned by wifi.

6) Add a new unconfined domain called dnsmasq.te, and allow
transitions from netd to that domain. Over time, we'll tighten up
the dnsmasq.te domain.

7) Add a new unconfined domain called hostapd.te, and allow
transitions from netd to that domain. Over time, we'll tighten up
the hostapd.te domain.

The net effect of these changes is to re-enable SELinux protections
for netd. The policy is FAR from perfect, and allows a lot of wiggle
room, but we can improve it over time.

Testing: as much as possible, I've exercised networking related
functionality, including turning on and off wifi, entering airplane
mode, and enabling tethering and portable wifi hotspots. It's quite
possible I've missed something, and if we experience problems, I
can roll back this change.

Bug: 9618347
Change-Id: I23ff3eebcef629bc7baabcf6962f25f116c4a3c0