Fix build-error (pointy hat; didn't merge full up-to-date code)

MFC after:	21 days
X-MFC-to:	stable/10 stable/9
X-MFC-with:	274116
Make libdpv [dpv(3)] WARNS=6 clean for clang on -CURRENT.
NB: aka unbreak the build

Reviewed by:	shurd
MFC after:	21 days
X-MFC-to:	stable/10 stable/9
X-MFC-with:	274116 274120
Extend struct ucred with group table.

This saves one malloc + free with typical cases and better utilizes
memory.

Submitted by:	Tiwei Bie <btw mail.ustc.edu.cn> (slightly modified)
X-Additional:	JuniorJobs project