This enables using echo_client with Bluetooth by passing
CONF_FILE=prj_bt.conf, it is also enabled for testing so changes to
echo_client are actually tested with NETWORKING_WITH_BT.
Change-Id: I1ff83a9d0049e121dc7e406656e3282b16ee8c91
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>