NFSD: Move svc_serv_ops::svo_function into struct svc_serv

[ Upstream commit 37902c63 ]

Hoist svo_function back into svc_serv and remove struct
svc_serv_ops, since the struct is now devoid of fields.

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