Bluetooth: Don't mask ECDH related events if CONFIG_BT_ECC disabled

It is related to b904ad38.
This fixes checking ECDH related events in event mask.
If ECDH support is disabled in host, there is no need to check
if those are supported in the controller.

Signed-off-by: Mariusz Skamra <mariusz.skamra@codecoup.pl>