SMP: Add error status in case of no L2CAP LCB's

Usecase:
1) Pair/Connect DUT with devices until MAX_L2CAP_LINKS is reached
2) Try to pair with new BLE Device.

Expected Result:
Pairing should fail gracefully since MAX_L2CAP_LINKS is reached

Observed Results:
Pairing stuck in repeated loop until BT off and on.

Root Cause:
Callback status is not updated with failure in case of error in
connecting L2CAP Fixed channel during SMP Pair due to unavailability
of LCB(s).

Fix:
Update the error code before sending SMP_AUTH_CMPL_EVT to SMP
state machine.

Test: Above usecase works fine after the change

Bug: 157326526
Change-Id: Idcee8869c4d87d4da98ce2ded95c97034f5f1b5c