net: fix dummy 'nf_conntrack_event_cache()'

The dummy version of 'nf_conntrack_event_cache()' (used when the
NF_CONNTRACK_EVENTS config option is not enabled) had not been updated
when the calling convention changed.

This was introduced by commit a71996fc


("netfilter: netns nf_conntrack: pass conntrack to
nf_conntrack_event_cache() not skb")

Tssk.

Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Patrick McHardy <kaber@trash.net>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>