NFSv4: include bitmap in nfsv4 get acl data

The NFSv4 bitmap size is unbounded: a server can return an arbitrary
sized bitmap in an FATTR4_WORD0_ACL request.  Replace using the
nfs4_fattr_bitmap_maxsz as a guess to the maximum bitmask returned by a server
with the inclusion of the bitmap (xdr length plus bitmasks) and the acl data
xdr length to the (cached) acl page data.

This is a general solution to commit e5012d1f "NFSv4.1: update
nfs4_fattr_bitmap_maxsz" and fixes hitting a BUG_ON in xdr_shrink_bufhead
when getting ACLs.

Fix a bug in decode_getacl that returned -EINVAL on ACLs > page when getxattr
was called with a NULL buffer, preventing ACL > PAGE_SIZE from being retrieved.

Cc: stable@kernel.org
Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
static void nfs4_xdr_enc_renew(struct rpc_rqst *req, struct xdr_stream *xdr,
			       struct nfs_client *clp)
{
	struct compound_hdr hdr = {
		.nops	= 0,
	};

	encode_compound_hdr(xdr, req, &hdr);
	encode_renew(xdr, clp, &hdr);
	encode_nops(&hdr);
}

static void nfs4_xdr_enc_renew(struct rpc_rqst *req, struct xdr_stream *xdr,
			       struct nfs_client *clp)
{
	struct compound_hdr hdr = {
		.nops	= 0,
	};

	encode_compound_hdr(xdr, req, &hdr);
	encode_renew(xdr, clp, &hdr);
	encode_nops(&hdr);
}
