dynamic_debug: fix undefined reference to `__netdev_printk'

dynamic_debug: fix undefined reference to `__netdev_printk'

Dynamic debug recently added support for netdev_printk.  It uses
__netdev_printk() to support this functionality.  However, when CONFIG_NET
is not set, we get the following error:

lib/built-in.o: In function `__dynamic_netdev_dbg':
(.text+0x9fda): undefined reference to `__netdev_printk'

Fix this by making the call to netdev_printk() contingent upon CONFIG_NET.
 We could have fixed this by defining netdev_printk() to a 'no-op' in the
!CONFIG_NET case.  However, this is not consistent with how the networking
layer uses netdev_printk.  For example, CONFIG_NET is not set,
netdev_printk() does not have a 'no-op' definition defined.

Signed-off-by: Jason Baron <jbaron@redhat.com>
Acked-by: Randy Dunlap <rdunlap@xenotime.net>
Cc: Greg KH <greg@kroah.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@google.com>