Introduce a net_radio_prop type for net. properties that can be
set by radio or system.
Introduce a system_radio_prop type for sys. properties that can be
set by radio or system.
Introduce a dhcp_prop type for properties that can be set by dhcp or system.
Drop the rild_prop vs radio_prop distinction; this was an early
experiment to see if we could separate properties settable by rild
versus other radio UID processes but it did not pan out.

Remove the ability to set properties from unconfineddomain.
Allow init to set any property.  Allow recovery to set ctl_default_prop
to restart adbd.

Change-Id: I5ccafcb31ec4004dfefcec8718907f6b6f3e0dfd
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>