nfscl: Restore sending the effective GID to the server

Fixes: be1f7435ef218b1d ("kern: start tracking cr_gid outside of cr_groups[]")
MFC after: 9 days
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D52256

(cherry picked from commit 71db32347665753a3384e36dcf89c9e3a8af6529)