Bluetooth: Host: Set scan option type to uint8_t

Changed the scan option type from uint32_t to
uint8_t.

There are 2 reasons for this:
1) This reduces the size of the struct bt_le_scan_param.
   Since we are now storing two copies of scan parameters
   statically in the host, this is not insignficant.
2) This fixes a "hole" in the struct. There are no longer
   3 empty octets between the `type` and the `options`, which
   caused valgrind warnings when using `memcpy` and `memcmp`
   of the struct.

Currently we only need 8 bits for the options available.
If additional options are added later, the field need
to be increased. For the above reasons some additional
refactoring my be required to avoid significant size
increases and the valgrind issue.

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