nfsd: fix NFS regression

nfsd: fix NFS regression

Fix regression introduced in pre-3.14 kernels by cherry-picking
aa07c713ecfc0522916f3cd57ac628ea6127c0ec (NFSD: Call ->set_acl with a
NULL ACL structure if no entries). This is in v3.12.22 as commit
723ac81c8671b3a095d9eb303974c7bc9964b506.

The affected code was removed in 3.14 by commit
4ac7249ea5a0ceef9f8269f63f33cc873c3fac61 (nfsd: use get_acl
and ->set_acl). The ->set_acl methods are already able to cope with a
NULL argument. So this is not needed for >= 3.14.

Signed-off-by: Sergio Gelato <Sergio.Gelato@astro.su.se>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>