net: Remove bogus reference to BUS_ID_SIZE in sysfs code.

BUS_ID_SIZE is really no more, and device names are dynamically
allocated and thus can be any necessary size.

So remove the BUG check here making sure BUS_ID_SIZE is at least
as large as IFNAMSIZ.

Signed-off-by: David S. Miller <davem@davemloft.net>