netfilter: connlabels: prefer static lock initialiser

seen during boot:
BUG: spinlock bad magic on CPU#2, swapper/0/1
 lock: nf_connlabels_lock+0x0/0x60, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
Call Trace:
 do_raw_spin_lock+0x14e/0x1b0
 nf_connlabels_get+0x15/0x40
 ct_init_net+0xc4/0x270
 ops_init+0x56/0x1c0
 register_pernet_operations+0x1c8/0x350
 register_pernet_subsys+0x1f/0x40
 tcf_register_action+0x7c/0x1a0
 do_one_initcall+0x13d/0x2d9

Problem is that ct action init function can run before
connlabels_init().  Lock has not been initialised yet.

Fix it by using a static initialiser.

Fixes: b57dc7c1 ("net/sched: Introduce action ct")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>