netdevice: Update netif_dbg for CONFIG_DYNAMIC_DEBUG

Make netif_dbg use dynamic debugging whenever
CONFIG_DYNAMIC_DEBUG is enabled.

commit b558c96f
("dynamic_debug: make dynamic-debug supersede DEBUG ccflag")
missed updating the netif_dbg variant.

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