Encrypt LE link immediately on reconnection

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

Ignore-AOSP-First: security
Test: mmm packages/modules/Bluetooth
Flag: com.android.bluetooth.flags.le_enc_on_reconnection
Bug: 362977693
Bug: 363033295
Change-Id: I607af8214f4fd9c3905f2e053ba136cd6189361f