[GD ACL] Make ACL packets non-flushable by default

* So that enhanced flush command does not discard pending ACL packets
that may be one of those A2DP commands

Bug: 177278022
Bug: 178752129
Test: gd/cert/run
Tag: #gd-refactor
Change-Id: Ibf168d0a022c8ef93058e0e986566b40c808e003