Ignore MIX_ROUTE_FLAG_DISALLOWS_PREFERRED_DEVICE in AIDL conversion

Ignored MIX_ROUTE_FLAG_DISALLOWS_PREFERRED_DEVICE in Audio Mix
Route Flag conversion since it is for internal use and not defined
in AIDL interface.

Bug: 407460384
Flag: EXEMPT bug fix
Test: atest com.google.android.gts.audio.AudioHostTest#testPolicyRegistration_isRegistere
Change-Id: I520930180fed3775b5a2c0a44755637a241ac474