nfsd: Fix sort_pacl in fs/nfsd/nf4acl.c to actually sort groups

nfsd: Fix sort_pacl in fs/nfsd/nf4acl.c to actually sort groups

We have been doing some extensive testing of Linux support for ACLs on
NFDS v4. We have noticed that the server rejects ACLs where the groups
are out of order, for example, the following ACL is rejected:

A::OWNER@:rwaxtTcCy
A::user101@domain:rwaxtcy
A::GROUP@:rwaxtcy
A:g:group102@domain:rwaxtcy
A:g:group101@domain:rwaxtcy
A::EVERYONE@:rwaxtcy

Examining the server code, I found that after converting an NFS v4 ACL
to POSIX, sort_pacl is called to sort the user ACEs and group ACEs.
Unfortunately, a minor bug causes the group sort to be skipped.

Signed-off-by: Frank Filz <ffilzlnx@us.ibm.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>