netfilter: remove the compat_{get,set} methods

All instances handle compat sockopts via in_compat_syscall() now, so
remove the compat_{get,set} methods as well as the
compat_nf_{get,set}sockopt wrappers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>