SMP MITM Security Request on encrypted link

Test steps
1. Connect over LE
2. Perform authenticated LE pairing
3. Disconnect
4. Reconnect as central
5. Wait for the link to be encrypted
6. Send SMP Security Request with MITM protection requirement

Expectation: The link is encrypted again. No repairing.

Bug: 295061381
Test: avatar run --include-filter="SmpTest"
Test: atest avatar -v
Change-Id: Ia1d7030e6cf604f57ea14663d99d678074c93894