setcred(): Fix RACCT resource accounting on credentials change

When credentials are changed, we need to adjust the sum of resources
associated to the initial and new process' user IDs (and old and new
login classes and jails, but setcred() does not change them) for them to
stay consistent.

PR: 290352
MFC after: 3 days
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D53457

(cherry picked from commit 2be5127c4a31bacac9b4158395bfa844f6033626)