Bluetooth: SMP: Ignore unsupported AuthReq in Security Request

If Security Request with unsupported flags is received just ignore them
instead of repairing. This is already done for Pairing Request but was
missing in Security Request.

Since we are still on 4.0 just remove any new bits definitions and update
BT_SMP_AUTH_MASK accordingly.

This fix constant repairing (instead of just enabling encryption) with
peripherals that support LE Secure Connections.

Change-Id: Ic053590755e97eadbcadbea788670c050f895d32
Signed-off-by: Szymon Janc <ext.szymon.janc@tieto.com>