[NETFILTER]: fix ebtable targets return

The function ebt_do_table doesn't take NF_DROP as a verdict from the targets.

Signed-off-by: Joonwoo Park <joonwpark81@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>