sunrpc: rename NFS_NGROUPS to UNX_NGROUPS for auth unix

NFS_NGROUPS has been move to sunrpc, rename to UNX_NGROUPS.

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>