freeradius3: add missing conffiles to Makefile

freeradius3: add missing conffiles to Makefile

Config files
/etc/freeradius3/policy.d/accounting
/etc/freeradius3/policy.d/filter
/etc/freeradius3/proxy.conf
/etc/freeradius3/sites-available/default
and link
/etc/freeradius3/sites-enabled/default
are in the freeradius3 package and are mentioned in the main config file
/etc/freeradius3/radiusd.conf
Thus, they must be explicitly specified in the Makefile.

File
/etc/freeradius3/sites/default
is not included in the package, is not created during installation,
is not mentioned in the main config file and should therefore be excluded
from the Makefile.

Signed-off-by: Alexey Dobrovolsky <dobrovolskiy.alexey@gmail.com>