nfsd: embed nfsd4_current_state in nfsd4_compoundres

Remove the allocation of struct nfsd4_compound_state.

Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>