cr_canseeothergids(): Policy change's manual pages impact

See previous commit that made cr_canseeothergids() use the new
realgroupmember() function, taking into account real group IDs instead
of effective ones.

PR: 272093
Reviewed by: pauamma_gundo.com, mhorne
MFC after: 2 weeks
Sponsored by: Kumacom SAS
Differential Revision: https://reviews.freebsd.org/D40644