[NETFILTER]: x_tables: move table->lock initialization

xt_table->lock should be initialized before xt_replace_table() call, which
uses it. This patch removes strict requirement that table should define
lock before registering.

Signed-off-by: Dmitry Mishin <dim@openvz.org>
Signed-off-by: Kirill Korotaev <dev@openvz.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>