xt_log.h: fix warning

In file included from net/ipv4/netfilter/ipt_LOG.c:28:
include/net/netfilter/xt_log.h: In function 'sb_close':
include/net/netfilter/xt_log.h:50: warning: value computed is not used
In file included from net/ipv6/netfilter/ip6t_LOG.c:27:
include/net/netfilter/xt_log.h: In function 'sb_close':
include/net/netfilter/xt_log.h:50: warning: value computed is not used

Signed-off-by: mechmetal <fullmetalmech@gmail.com>
Signed-off-by: nobodyAtall <tsogkas@ceid.upatras.gr>