Bluetooth: Add proper defines for HCI connection role

All HCI commands and events, including LE ones, use 0x00 for master role
and 0x01 for slave role. It makes therefore sense to add generic defines
for these instead of the current LE_CONN_ROLE_MASTER. Having clean
defines will also make it possible to provide simpler internal APIs.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>