Bluetooth: controller: Validate disconnect reason in disconnect command

Validate the disconnect reason in the disconnect command, according
to the the core specification.

7.1.6 Disconnect command:
Authentication Failure error code (0x05), Other End Terminated Connec-
tion error codes (0x13 to 0x15), Unsupported Remote Feature error code
(0x1A), Pairing with Unit Key Not Supported error code (0x29) and Unac-
ceptable Connection Parameters error code (0x3B).

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>