Bluetooth: Controller: Fix drift compensation on connection update

Fix drift compensation applied late under high throughput at
after the instant has passed for a connection update.

Workaround test failures due to Zephyr Controller scheduling
overlap causing Periodic Advertising Sync timeouts, ACL
connection failed to be established or Controller assertion
when having latency at the CIS setup instant.

Workaround by using `-start_offset` to ensure that the ACL
established does not overlap the sink being established.

Relates to commit 5f852998 ("tests: bsim: Bluetooth:
Workaround Zephyr Controller scheduling overlap").

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>