iiod/init/iiod.service.cmakein: Add support for extra iiod options
iiod/init/iiod.service.cmakein: Add support for extra iiod options

This patch adds support to source iiod options via /etc/default/iiod

Signed-off-by: Michael Hennerich <38f18d03059a1bc88082b55d7ca2d9b1ebfaffe0@analog.com>

analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio