floss: Change api to set_default_event_mask_except

The suspend implementation in Floss wants to mask away some events to
prevent spurious wakes. This change updates the btif api
|set_default_event_mask| to also accept bit masks that will be disabled
from the final event mask that is sent to the controller.

As part of this change, suspend will now stop calling |clear_event_mask|
during suspend and instead will just disable the Disconnect and Mode
change events only.

Bug: 231345733
Tag: #floss
Test: Manual test on ChromeOS.
Change-Id: I0105085c465666e5a8c0e7890c36072234fe05e2