netfilter: cttimeout: ctnl_timeout_find_get() returns incorrect pointer to type

Compiler did not catch incorrect typing in the rcu hook assignment.

 % nfct add timeout test-tcp inet tcp established 100 close 10 close_wait 10
 % iptables -I OUTPUT -t raw -p tcp -j CT --timeout test-tcp
 dmesg - xt_CT: Timeout policy `test-tcp' can only be used by L3 protocol number 25000

The CT target bails out with incorrect layer 3 protocol number.

Fixes: 6c1fd7dc ("netfilter: cttimeout: decouple timeout policy from nfnetlink_cttimeout object")
Reported-by: Harsha Sharma <harshasharmaiitr@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>