Bluetooth: EWS: rewrite handling SAR bits

Segmentation and Reassembly (SAR) occupies different windows in standard and
extended control fields. Convert hardcoded masks to relative ones and use shift
to access SAR bits.

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>