Conclude the LE encryption request immediately if already encrypted.

Some devices may not respond to the SMP Security request if the link is already encrypted. Non-response for SMP Security requests is treated as a pairing failure by SMP, resulting in bond removal.
This change reduces the probability of such issues.

Change-Id: Ib74f84bcc3965fee25b0ad86a1980aa0e08e9080
Test: mmm packages/modules/Bluetooth
Flag: EXEMPT bugfix
Bug: 384575786