netfilter/ebtables: clean up compat {get, set}sockopt handling

Merge the native and compat {get,set}sockopt handlers using
in_compat_syscall().  Note that this required moving a fair
amout of code around to be done sanely.

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