NFSD: Remove "inline" directives on op_rsize_bop helpers

[ Upstream commit 6604148c ]

These helpers are always invoked indirectly, so the compiler can't
inline these anyway. While we're updating the synopses of these
helpers, defensively convert their parameters to const pointers.

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