lock_delay(9): improve interaction with restrict_starvation

After e7a5b3bd058, the la->delay value was adjusted after
being set by the starvation_limit code block, which is wrong.

Reported By: avg
Reviewed By: avg
Fixes: e7a5b3bd058
Sponsored By: NetApp, Inc.
Sponsored By: Klara, Inc.
Differential Revision: https://reviews.freebsd.org/D29513