net/atm: remove the atmdev_ops {get, set}sockopt methods

[ Upstream commit a06d30ae7af492497ffbca6abf1621d508b8fcaa ]

All implementations of these two methods are dummies that always
return -EINVAL.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: ec79003c5f9d ("atm: atmtcp: Prevent arbitrary write in atmtcp_recv_control().")
Signed-off-by: Sasha Levin <sashal@kernel.org>