NFSD: fix endianness issue in nfsd4_encode_fattr4

The nfs4 mount fails with EIO on 64-bit big endian architectures since
v6.7. The issue arises from employing a union in the nfsd4_encode_fattr4()
function to overlay a 32-bit array with a 64-bit values based bitmap,
which does not function as intended. Address the endianness issue by
utilizing bitmap_from_arr32() to copy 32-bit attribute masks into a
bitmap in an endianness-agnostic manner.

Cc: stable@vger.kernel.org
Fixes: fce7913b

 ("NFSD: Use a bitmask loop to encode FATTR4 results")
Link: https://bugs.launchpad.net/ubuntu/+source/nfs-utils/+bug/2060217
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>