Bluetooth: controller: Make random force on lost anchor configurable

Legacy functionality in ull_conn will force scheduling of a connection
which has missed an anchor point due to lost RX. This kicks in either
for previously skipped events (latenzy_event != 0) or at random
depending on the randomness of the AA bit pattern.

This behavior is good at ensuring that a connection with errors or
aborted RX gets prioitized, and helps break locked round-robin
patterns with lost sync, but it also breaks the predictability of
the round-robin ticker scheduling.

With "must_expire" enabled, this feature also kicks in for scheduling
collisions, which may not be desirable.

This commit adds a configuration flag, BT_CTLR_CONN_RANDOM_FORCE, which
is default enabled (legacy behavior).

Signed-off-by: Morten Priess <mtpr@oticon.com>