rtnl: fix the loop index update error in rtnl_dump_ifinfo()

If the link is filtered out, loop index should also be updated. If not,
loop index will not be correct.

Fixes: dc599f76

 ("net: Add support for filtering link dump by master device and kind")
Signed-off-by: Zhang Shengju <zhangshengju@cmss.chinamobile.com>
Acked-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>