netfilter: ebtables: only call xt_compat_add_offset once per rule

The optimizations in commit 255d0dc3
(netfilter: x_table: speedup compat operations) assume that
xt_compat_add_offset is called once per rule.

ebtables however called it for each match/target found in a rule.

The match/watcher/target parser already returns the needed delta, so it
is sufficient to move the xt_compat_add_offset call to a more reasonable
location.

While at it, also get rid of the unused COMPAT iterator macros.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>