netdevice.h: Add __cold to netdev_<level> logging functions

Add __cold to the netdev_<level> logging functions similar to
the use of __cold in the generic printk function.

Using __cold moves all the netdev_<level> logging functions
out-of-line possibly improving code locality and runtime
performance.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>