NFSD: Replace boolean fields in struct nfsd4_copy

[ Upstream commit 1913cdf5 ]

Clean up: saves 8 bytes, and we can replace check_and_set_stop_copy()
with an atomic bitop.

[ cel: adjusted to apply to v5.10.y ]
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>