Fix for Bluetooth connection being dropped after HCI Read Encryption Key Size

If remote device stop the encryption before we call "Read Encryption Key Size",
we might receive Insufficient Security, which means that link is no longer
encrypted.

In such cases we should stay connected, rather than disconnecting the
link.

Test: Connect to device that stop encryption right after encryption is
complete, i.e. to change roles.
Bug: 124301137
Bug: 132626699

Change-Id: Iab0fd9f357d18a6b048b971d0393fbb47fd4d793