This enables using coap_server with Bluetooth by passing
CONF_FILE=prj_bt.conf, it is also enabled for testing so changes to
coap_server are actually tested with NETWORKING_WITH_BT.
Change-Id: I58b286520da0e0e4cba77dd52ea3f64f0268582a
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>