(Reland) Encrypt LE link immediately on reconnection

LE link must be encrypted immediately on connection if device are
already bonded.

This is a backport of ag/29056565, but the code needs to go in a
different location because that patch relies on recent feature work.

Ignore-AOSP-First: security
Test: mmm packages/modules/Bluetooth
Bug: 288144143
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:d254a228ebc58cb7eb1470faf506e5b722cea096)
Merged-In: Ib9075586ed08eceac917909f2c07d54f7702901f
Change-Id: Ib9075586ed08eceac917909f2c07d54f7702901f