Bluetooth: GATT: Update gatt.h _value doc description

The _value in BT_GATT_ATTRIBUTE was misleading as
it cannot be generically used a attribute value,
and actually is a user_data pointer.

The macros BT_GATT_CPF, BT_GATT_CEP and BT_GATT_CUD was
also update to more accurate describe the expected
type of value for the macros.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>
1 file changed