sysctl: expose all net/core sysctls inside netns

All were not visible to the non-priv users inside netns. However,
with 4ecb9009 ("sysctl: allow override of /proc/sys/net with
CAP_NET_ADMIN"), these vars are protected from getting modified.
A proc with capable(CAP_NET_ADMIN) can change the values so
not having them visible inside netns is just causing nuisance to
process that check certain values (e.g. net.core.somaxconn) and
see different behavior in root-netns vs. other-netns

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Mahesh Bandewar <maheshb@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/sysctl_net_core.c

@@ -643,11 +643,6 @@ static __net_init int sysctl_core_net_init(struct net *net)
 
 		for (tmp = tbl; tmp->procname; tmp++)
 			tmp->data += (char *)net - (char *)&init_net;
-
-		/* Don't export any sysctls to unprivileged users */
-		if (net->user_ns != &init_user_ns) {
-			tbl[0].procname = NULL;
-		}
 	}
 
 	net->core.sysctl_hdr = register_net_sysctl(net, "net/core", tbl);