rtnl: RTM_GETNETCONF: fix wrong return value

rtnl: RTM_GETNETCONF: fix wrong return value

BugLink: http://bugs.launchpad.net/bugs/1553179
[ Upstream commit a97eb33ff225f34a8124774b3373fd244f0e83ce ]

An error response from a RTM_GETNETCONF request can return the positive
error value EINVAL in the struct nlmsgerr that can mislead userspace.

Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>