net: Initialise net.core sysctl defaults in preinit_net().

net: Initialise net.core sysctl defaults in preinit_net().

Commit 7c3f1875c66f ("net: move somaxconn init from sysctl code")
introduced net_defaults_ops to make sure that net.core sysctl knobs
are always initialised even if CONFIG_SYSCTL is disabled.

Such operations better fit preinit_net() added for a similar purpose
by commit 6e77a5a4af05 ("net: initialize net->notrefcnt_tracker earlier").

Let's initialise the sysctl defaults in preinit_net().

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>