hack(ble): Temporarily silence a warning

With the increased warning-level, GCC warns about three unused fields in
`bleSmpCfg`:

    - maxAttemptTimeout: Maximum 'Repeated attempts' timeout in msec
    - attemptDecTimeout: Time msec before attemptExp decreases
    - attemptExp: Exponent to raise attemptTimeout on maxAttempts

These should probably be set to sensible values but to make !360
mergeable, explicitly set them to zero for now.

Signed-off-by: Rahix <rahix@rahix.de>