NFSD: Add an nfsd4_read::rd_eof field

[ Upstream commit 24c7fb85 ]

Refactor: Make the EOF result available in the entire NFSv4 READ
path.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>