NFS: Move common includes outside ifdef

module.h, clnt.h, addr.h and dns_resolve.h is always included whether
CONFIG_NFS_USE_KERNEL_DNS is set or not and their order does not seems
to matter.

Move them outside the ifdef to simplify code and avoid checkincludes
message.

Signed-off-by: GUO Zihua <guozihua@huawei.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>