rtnetlink: make rtnl_fill_link_ifmap() RCU ready

Use READ_ONCE() to read the following device fields:

	dev->mem_start
	dev->mem_end
	dev->base_addr
	dev->irq
	dev->dma
	dev->if_port

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>