Encrypt BR/EDR link immediately after pairing

In the peripheral role stack does not immediately encrypt the link after BR/EDR pairing. Instead it tries to change the role first. If the role change fails, the link is not encrypted. Some remote devices don't like to concede the central role.
Secured service access would eventually force the encryption but it delays potential CTKD and service discovery.

Test: mmm packages/modules/Bluetooth
Flag: com.android.bluetooth.flags.immediate_encryption_after_pairing
Bug: 401192310
Bug: 402510244
Change-Id: I9a31ae46cb80b3bb42c6f4b0fbf957fb83876db1