Bluetooth: Refactor service discovery filter logic

This patch refactor code responsible for filtering when service
discovery method is used. Previously this code was mixed with
mgmt_device found logic. Now when it's in one place whole logic can
be greatly simplified. That includes removing no longer necessary
length field and merging checks for eir and scan_rsp.

Signed-off-by: Jakub Pawlowski <jpawlowski@google.com>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>