net: Push capable(CAP_NET_ADMIN) into the rtnl methods

- In rtnetlink_rcv_msg convert the capable(CAP_NET_ADMIN) check
  to ns_capable(net->user-ns, CAP_NET_ADMIN).  Allowing unprivileged
  users to make netlink calls to modify their local network
  namespace.

- In the rtnetlink doit methods add capable(CAP_NET_ADMIN) so
  that calls that are not safe for unprivileged users are still
  protected.

Later patches will remove the extra capable calls from methods
that are safe for unprivilged users.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_netlink.c

@@ -240,6 +240,9 @@ int br_setlink(struct net_device *dev, struct nlmsghdr *nlh)
 	struct nlattr *tb[IFLA_BRPORT_MAX];
 	int err;
 
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
 	ifm = nlmsg_data(nlh);
 
 	protinfo = nlmsg_find_attr(nlh, sizeof(*ifm), IFLA_PROTINFO);