btif/osi: move I/O to OSI layer. disable for multi-user.

Two issues here.
    One, read/write/modify/remove access to the checksum by the secondary user.
    Two, Fail to access keystore with secondary user stack running (stack doesn't run as UID 1002)

Bug: b/125452367
Test: atest net_test_btif net_test_bluetooth net_test_osi
Change-Id: I7af452e00a4f342f1c49006e86488b59195b70ce